Depletion and Reaccumulation of Follicular Thyroglobulin (TG) in Guinea-Pig Thyroid Gland after Short- and Long-Term Administration of Thyrotropin (TSH)

The relationships among the content and composition of soluble iodoproteins in thyroid gland, the serum Tg concentration and the morphological structure of gland were investigated in guinea-pigs during short-term and long-term TSH administration (2 I.U. per day for 1 to 28 days). A significant decrease in the content of Tg in the gland (from 6.50 mg to 1.32 mg/100 mg tissue), disappearance of 12 S iodoprotein, hypertrophy and hyperplasia of the follicular cells were observed in guinea-pigs treated with TSH up to 7 days. Later on, after depletion of follicular colloid, reaccumulation of colloid in the preexisting and newformed follicles (a marked increase of Tg and 12 S protein) and partial involution of the structural changes occurred. The serum Tg concentration increased during the whole period of TSH treatment (mean values from 100 to 500 micrograms/l). A marked positive correlation between serum Tg concentration and thyroid weight was found. Serum T3 and T4 concentrations increased transiently with maximal values on the 1st day (T3, from 0.86 to 3.26 nmol/l, T4, from 44 to 138 nmol/l) and decreased thereafter. The results imply that different regulatory mechanisms exist which control thyroid hormone secretion and transfer of Tg from the gland into blood circulation. The serum Tg level is directly dependent on the total bulk of thyroid tissue, but is considerably less dependent on the structure of the gland. The reaccumulation of colloid (Tg) in thyroid follicles of guinea-pigs treated with TSH is a result of the reduction of the stimulatory effect of TSH on the process of Tg degradation during chronic hormone application. Several different factors may be responsible for the appearance of refractoriness or desensitization of the thyroid to prolonged exogenous TSH stimulation.

Primary congenital hypothyroidism: defects in iodine pathways

The thyroid gland is the only source of thyroid hormone production. Thyroid hormone is essential for growth and development, and is of special importance for the development of the central nervous system. It was for that reason that neonatal screening on congenital hypothyroidism was introduced and is now performed in many countries. Defects in thyroid hormone production are caused by several disorders in hormone synthesis and in the development of the thyroid gland (primary hypothyroidism) or of the pituitary gland and hypothalamus (central hypothyroidism). This paper describes defects in the synthesis of thyroid hormone caused by disorders in the synthesis or iodination of thyroglobulin, leakage of iodinated proteins by a stimulated thyroid gland and the presence of abnormal iodoproteins, mainly iodinated albumin, in the thyroid gland and blood circulation. Circulating thyroglobulin and abnormal iodoproteins, as well as the breakdown products of these iodoproteins excreted in urine, are used for etiological diagnosis and classification. Moreover, our finding of an enzyme that catalyses the dehalogenation of iodotyrosines, which is important for iodine recycling and required for economical use of iodine, is also referred to.

Identification of iodinated proteins in cultured thyrocytes and their possible significance for thyroid hormone formation

The thyroid gland is known to generate the iodinated hormones T3 and T4 from the prohormone thyroglobulin. In this report we examined whether polypeptides other than thyroglobulin are iodinated and hormonogenic in thyrocytes and the prerequisites for their iodination. In primary cultures of porcine thyrocytes, a substantial portion of organified radioiodine was incorporated into cellular proteins other than thyroglobulin. Some of these were identified by immunoprecipitation. They included proteins of the extracellular matrix, plasma membrane proteins, and lysosomal enzymes, which follow in part a secretion and recapture pathway. All of these proteins come into contact with the iodinating system of thyrocytes located on the apical plasma membrane and possess iodination consensus sequences. Immunoprecipitation with T3- or T4-specific antibodies showed that thyroid hormones were detectable only within thyroglobulin. This was confirmed by an analysis of the iodoamino acids of thyroglobulin, cathepsin-D (representing a secretory protein), and aminopeptidase-N (a membrane-integrated protein) by two-dimensional TLC, which revealed the presence of T3 and T4 only within the polypeptide chain of thyroglobulin. These results indicate that iodoproteins other than thyroglobulin do not participate in the generation of thyroid hormones in situ.

Low-molecular-weight iodoproteins in the congenital goiters of cog/cog mice

Previously we described sedimentation and immunologic abnormalities of thyroglobulin (Tg) in a strain of mice with inherited congenital goiter and hypothyroidism (cog/cog). The goals of the present study were to determine the extent to which thyroid gland stimulation by TSH accounts for the abnormal properties of cog/cog Tg and to characterize further the abnormally small iodoproteins found in cog/cog mice. Cog/cog and control +/cog and BALB/c mice were fed with either normal or thyroid-hormone-containing diets and were injected with Na125I. Sucrose density gradient centrifugation of labeled thyroid extracts from cog/cog mice on normal diet showed that 82% of the iodine was in iodoproteins smaller than Tg, with sedimentation rates of 3-8S. No 12S and 19S peaks, characteristic of normal Tg, were present, but distinct and stable 12S and 19S peaks emerged after recentrifugation of the 12S and 19S areas. In contrast, in cog/cog mice treated with T4, a smaller (55%) amount of 3-8S iodoproteins and distinct 12S and 19S peaks were present. In both groups of mice, the labeled 3-8S iodoproteins were composed of three fractions: 15% precipitated by antirat Tg serum, 38% precipitated by antimouse albumin serum, and 47% not precipitated by either serum. The 3-8S iodoproteins contained labeled MIT and DIT and no T4. On sodium dodecyl sulfate polyacrylamide gel electrophoresis the 3-8S iodoprotein fraction that reacted with anti-Tg serum contained a distinct electrophoretic band at 49K. The 3-8S nonreactive iodoproteins resolved into several bands of lower molecular weight. We conclude that the 3-8S iodoproteins in cog/cog mice are heterogeneous and that TSH stimulation contributes to the production of these low-molecular-weight iodoproteins.

Age-related accumulation of lysosomes and other cytological features in active thyroid follicles of the CBA mouse

This study attempts to elucidate the mechanism through which lysosomal accumulation occurs with age in the epithelial cells of the thyroid gland and especially in the "active" follicles of the aging mouse thyroid. Thyroid morphology and function in old CBA (at least 24 months of age) male mice were compared with those in young (2 months of age) animals. The effects of different intake of iodine were tested and compared in both cohorts, each of which was divided into three groups: (i) low iodine group, (ii) moderate iodine group, and (iii) high iodine group. As expected, the present work confirmed the well-known accumulation with age of "cold" follicles coexisting with "active" follicles in the old mouse thyroid. Attention has been focused on the active follicles whose follicular cells contained in their cytoplasm a large number of pleomorphic dense bodies. The lysosomal nature of these bodies, referred to as secondary lysosomes, was confirmed by histochemistry; however, they displayed variability in acid phosphatase staining. In old animals, regardless of the type of iodine regimen, the ratio between relative follicular volume and relative colloid volume as determined by morphometry remained unchanged. Ultrastructurally, the relative volume occupied by secondary lysosomes in "active" follicles was always higher than in the young groups. Autoradiographic studies with 125I revealed that a large part of the radioactivity was located in secondary lysosomes of thyroid cells in "active" follicles of old mice when radioiodine was injected 3 weeks before death. Two different types of vacuoles were present in a non-negligible number of thyrocytes of the "active" follicles in aged cohorts. The first type was made up of grossly dilated rough endoplasmic cisternae, the second corresponded to intracytoplasmic microfollicular vacuoles. Both aspects have been described in conditions of chronic stimulation. It is concluded (1) that different intake of iodine for 6 weeks does not modulate the thyroid morphology in old mice; (2) that in the thyrocytes of the "active" follicles in old mice accumulation of secondary lysosomes occurs due to a slowdown of turnover; and (3) that the follicular cells of "active" follicles feature morphological aspects suggesting a hyperactive state compensating the lack of hormone production in the "cold" follicles.

Proteolytic processing of thyroglobulin by extracts of thyroid lysosomes

The release of T4 and T3 from the prohormone thyroglobulin (Tg) occurs in thyroid lysosomes. To examine the role of cathepsin-B, -D, and -L, the three major endopeptidases in this process, we incubated rabbit [125I]Tg, labeled in vivo, with lysosomal extracts from human thyroids. Iodopeptide formation was evaluated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate after short term incubations (20-45 min), while iodoamino acid release was assessed by paper chromatography after long term incubations (8 and 24 h). Using pepstatin to inhibit cathepsin D, Z-Phe-Ala-CHN2 to inhibit both cathepsin B and L, and Z-Phe-Phe-CHN2 to selectively inhibit cathepsin L, we obtained the following results: 1) blocking of all three endopeptidases reduced both iodopeptide formation in short term experiments and iodoamino acid release in long term experiments by 80-90%; 2) iodopeptide formation was reduced by 85% with Z-Phe-Ala-CHN2, by 56% with Z-Phe-Phe-CHN2, and by 26% with pepstatin; 3) iodoamino acid release was reduced by 60-80% with Z-Phe-Ala-CHN2 and by 40-50% with either Z-Phe-Phe-CHN2 or pepstatin at 8 h, but by less than 20% at 24 h; pepstatin and Z-Phe-Phe-CHN2 together reduced iodoamino acid release by 80% and 60% at 8 and 24 h, respectively. Limited hydrolysis of Tg by lysosomal enzymes produced at least eight peptide fragments of less than 100,000 mol wt. Three of these, together representing 32% of the 125I released, resulted from cleavages in the C-terminal region of Tg corresponding to residues 2487, 2393, and 2390 of cDNA-derived human Tg. Several other peptides, together containing 38% of the 125I released, included the N-terminus of Tg. These C-terminal and N-terminal fragments contained three of Tg's four major hormonogenic sites, but none of the cleavage sites fell close to the hormone sites themselves. We conclude that 1) the formation of discrete iodopeptides precedes the release of iodothyronines and iodotyrosines from Tg; 2) the cysteine proteinases are more important than cathepsin D in this process; and 3) these endopeptidases selectively cleave Tg to favor the production of hormone-containing intermediates for subsequent processing by exopeptidases.

Changes in cAMP-dependent and Ca2(+)-phospholipid-dependent protein kinase activities in suspension cultures of porcine thyroid cells

The morphological and functional characteristics and the activities of cyclic AMP- (PKA I and PKA II) and calcium and phospholipid-dependent (PKC) protein kinases were studied in 2-day-old suspension cultures of porcine thyroid cells and were compared with those in freshly dissociated cells and intact glands. Thyroid cell morphology changed during the 2-day culture in the absence of specific regulators. This is characterized by a loss of cellular polarity, exo- and endocytotic vesicles and membranes of the rough endoplasmic reticulum, and an increase in the number of lysosomes, pseudomyelinic structures, lipidic inclusions and free ribosomes. Functional changes are characterized by a progressive decrease in protein iodination and its sensitivity to TSH stimulation. The total PKA activity in the cytosols of these cultures was slightly greater than that of freshly prepared tissue, due to the selective and significant accumulation of PKA I in cultured cells. In the particulate fraction the PKA activity was unchanged. PKC is the major kinase activity in porcine thyroids, and remains so in cultured cells. The slight drop in its activity in cytosols was offset by a significant increase in the particulate fraction, suggesting an intracellular redistribution of this kinase in cultured cells. The PKC activity is also partly activated in both the cytosol and particulate fraction, which results in an increased basal activity. The changes in PKA and PKC activities greatly modified the PKC/PKA ratios in the cytosols and the particulate fractions of cultured cells. These modifications could be partly responsible for the changes in sensitivity of cultured cells to the agents which control their activity.

Porcine neutrophil function in the presence of virulent and avirulent Salmonella choleraesuis

Porcine polymorphonuclear leukocytes (PMNLs) may be activated by bacteria to begin phagocytosis followed by oxidative and non-oxidative mechanisms of killing. The purpose of this study was to identify differences between virulent and avirulent Salmonella choleraesuis (S. choleraesuis) strains, 38 and 9 respectively, in their interactions with porcine PMNLs using five different assays. (1) Staphylococcus aureus (S. aureus) ingestion was determined by exposure of porcine PMNLs to a mixture of S. choleraesuis and 125I labeled S. aureus. There was a 2.98% and 22.20% decrease in S. aureus ingestion by mouse-avirulent S. choleraesuis 9 and mouse-virulent S. choleraesuis 38 respectively. (2) Iodination of proteins was done by exposing zymosan stimulated porcine PMNLs to S. choleraesuis in the presence of 125I and measuring its incorporation into porcine PMNL proteins. This assay indicated a 73.7% and 74.7% decrease in iodination by S. choleraesuis 9 and S. choleraesuis 38, respectively. (3) Cytochrome c reduction was performed by using porcine PMNLs, zymosan, and S. choleraesuis to determine the bacterial effect on superoxide anion production. S. choleraesuis 9 and S. choleraesuis 38 inhibited superoxide anion production by 78.0% and 92.6%, respectively. (4) Lactoferrin release from porcine PMNLs was measured by an ELISA using the supernatant from the cytochrome c assay. Results indicate a 52.0% and 61.0% increase in lactoferrin release by S. choleraesuis 9 and 38 respectively. (5) The bactericidal assay was performed by counting cfus of S. choleraesuis after preliminary incubation with porcine PMNLs, followed by killing of extracellular S. choleraesuis and lysis of porcine PMNLs. Survival of S. choleraesuis 9 and E. coli (control) were 7.50% and 1.37%, respectively, in contrast to 52.62% survival of the virulent S. choleraesuis 38. These results indicate that both strains inhibited protein iodination and caused a slight increase in lactoferrin release, but the virulent S. choleraesuis 38 inhibited S. aureus ingestion, cytochrome c reduction, and survived porcine PMNL killing more effectively than the avirulent S. choleraesuis 9.

Binding of monoiodinated neuropeptide Y to hippocampal membranes and human neuroblastoma cell lines

Monoiodinated radioligands of the homologous 36-amino acid peptides, neuropeptide Y (NPY) and peptide YY, were prepared by reverse phase high performance liquid chromatography with isocratic elution. [125I-Tyr1]- and [125I-Tyr36]monoiodoNPY bound equally well to a single class of high affinity binding sites on synaptosomal membranes prepared from porcine hippocampus (Kd = 1.0 X 10(-10) M) whereas iodine substitution in Tyr27, for example, partly interfered with the receptor binding. The receptors on the hippocampal membranes did not distinguish between neuropeptide Y and peptide YY either in their monoiodinated or in their unlabeled forms. Six out of twelve human neuroblastoma cell lines had high affinity binding sites for monoiodinated NPY ranging from 2 to 145 X 10(3) sites per cell. The NPY binding to three of the cell lines, SMS-MSN, SMS-KAN, and CHP-234 was of relatively high affinity (Kd = 1.3 to 6.1 X 10(-10) M), and, as in the hippocampal membranes, the long C-terminal fragment, NPY(13-36)peptide was also a relatively potent ligand for these receptors. Two other neuroblastoma cell lines, MC-IXC and CHP-212, expressed NPY receptors characterized by a lower affinity (Kd = 4.8 and 24.6 X 10(-9) M) and negligible cross-reactivity with the C-terminal fragment. It is concluded that monoiodinated radioligands of the tyrosine-rich neuropeptide Y can be prepared and that receptors for these ligands in two apparently different subtypes are found on a series of human neuroblastoma cell lines.

Hormone synthesis in human thyroglobulin: possible cleavage of the polypeptide chain at the tyrosine donor site

At moderate iodination levels (20 iodine atoms/mol) human thyroglobulin (hTg) produces after reduction a hormone-rich peptide of 26 kDa which contains the preferential hormonogenic 'acceptor' tyrosine (Tyr 5) of the protein. The site of cleavage of the hTg chain was demonstrated by analysis of the 26 kDa tryptic hydrolysis products. It consistently yielded the peptide Gln-82-Val-129 which consequently made it possible to localize the hTg chain cleavage at tyrosine residue 130. Evidence for tyrosine involvement in hTg cleavage during thyroid hormone formation supports the hypothesis that peptide bond cleavage would occur at the 'donor' tyrosine residue and suggests that tyrosine 130 would be the donor site reacting with the major hormone-forming acceptor site (Tyr 5) of hTg.

A quantitative model of traffic between plasma membrane and secondary lysosomes: evaluation of inflow, lateral diffusion, and degradation

We present here a mathematical model that accounts for the various proportions of plasma membrane constituents occurring in the lysosomal membrane of rat fibroblasts (Draye, J.-P., J. Quintart, P. J. Courtoy, and P. Baudhuin. 1987. Eur. J. Biochem. 170: 395-403; Draye, J.-P., P. J. Courtoy, J. Quintart, and P. Baudhuin. 1987. Eur. J. Biochem. 170:405-411). It is based on contents of plasma membrane markers in purified lysosomal preparations, evaluations of their half-life in lysosomes and measurements of areas of lysosomal and plasma membranes by morphometry. In rat fibroblasts, structures labeled by a 2-h uptake of horseradish peroxidase followed by a 16-h chase (i.e., lysosomes) occupy 3% of the cellular volume and their total membrane area corresponds to 30% of the pericellular membrane area. Based on the latter values, the model predicts the rate of inflow and outflow of plasma membrane constituents into lysosomal membrane, provided their rate of degradation is known. Of the bulk of polypeptides iodinated at the cell surface, only 4% reach the lysosomes every hour, where the major part (integral of 83%) is degraded with a half-life in lysosomes of integral to 0.8 h. For specific plasma membrane constituents, this model can further account for differences in the association to the lysosomal membrane by variations in the rate either of lysosomal degradation, of inflow along the pathway from the pericellular membrane to the lysosomes, or of lateral diffusion.

Monoiodotyrosine formation during thyroglobulin processing in Golgi vesicles

A golgi-enriched subfraction was obtained from porcine thyroid glands by differential centrifugation. When incubated in a suitable medium, these vesicles were able to concentrate iodide from the medium and bind it to protein. The iodination process was inhibited by methylmercapto-imidazole and was increased by the addition of an H2O2 generating system to the medium. Analysis of the protein content of the vesicles revealed the presence of 18 and 12-13 S thyroglobulin molecules, lacking mannose residues, and containing only monoiodotyrosine. It is concluded that in vitro, iodination can begin before exocytosis, in the smooth-surfaced vesicles derived from the golgi apparatus, as soon as N-acetylglucosamine is incorporated onto the pre-thyroglobulin molecule.

Why do total-body decay curves of iodine-labeled proteins begin with a delay?

The initial delay that occurs in total-body radiation curves reaching their single-exponential slopes was analyzed from 106 experiments involving several mammalian species (guinea pig, mouse, rabbit, and rat) and plasma proteins (alpha 1-acid glycoprotein, antithrombin III, fibrinogen, immunoglobulin G, and transferrin) in 14 different combinations. The time interval (Td) between injection and the intercept of the slope with the full-dose value was adopted as a measure of curve nonideality. The overall mean Td was 6.6 h, but individual values showed a significant correlation to protein half-lives, whereby proteins of unequal metabolic properties exhibited different mean Td values. Targeting protein to the liver abolished delay. Choice of the isotope (125I or 131I) and size of the labeled protein had no influence on the magnitude of delay. Whole-body radiation curves of animals that received [125I]iodotyrosines, Na131I, or 131I-polyvinylpyrrolidone exhibited no initial delays. These results do not support the earlier notion that delay is caused by a redistribution of the labeled protein in the body to radiometrically more favorable sites. However, they are compatible with the assumption that delayed passage of a protein dose through the extracellular matrix and/or retarded transfer of proteolytic products from extravascular catabolic sites to plasma may be responsible for the phenomenon.

Receptor binding of selectively labeled (Tyr-10) and (Tyr-13)-mono-125I-glucagons and competition by homologous 127I-labeled isomers

Two monoiodinated derivatives of glucagon were prepared by lactoperoxidase catalyzed iodination followed by separation on reverse-phase high-performance liquid chromatography. The purified (Tyr-10) and (Tyr-13)-mono-125I-labeled glucagon isomers were characterized and studied with respect to their binding to the receptors of isolated intact rat hepatocytes. The extent of steady-state binding to cellular receptor sites differed for the two labeled glucagon tracers at 37 degrees C as well as at 15 degrees C with (Tyr-10)-mono-125I-glucagon displaying higher receptor binding. The apparent equilibrium constants, Kd,app at 37 degrees C are 3.6 +/- 0.4 nM (mean +/- S.E. of three independent experiments) for the tyrosine-13-labeled tracer and 5.9 +/- 0.6 nM for the tyrosine-10-labeled glucagon with native glucagon as competitor. Since the observed Kd in the competition assay is a function of the true Kd values of the monoiodinated radioactive glucagon isomers and native glucagon, the dissociation constants were also measured with chemically identical tracer and competitor. Under these conditions, we obtained Kd values of 1.3 +/- 0.2 nM for the tyrosine-10-labeled analog and 2.0 +/- 0.2 nM for the tyrosine-13-labeled glucagon isomers confirming the higher receptor binding affinity of (Try-10)-mono-125I-glucagon. All competition curves fit the mathematical expression for a model of non-cooperative binding to a single class of receptors.

Autoregulation of iodide transport in the rabbit: absence of autoregulation in fetal tissue and comparison of maternal and fetal thyroid iodination products

Maternal and fetal rabbit thyroid glands were compared as to their ability to respond to excess iodide in vitro with a reduction in subsequent iodide transport activity. Preincubation of maternal thyroid tissue slices for 2 h with excess iodide (30 microM) resulted in a 31% reduction in the subsequently measured thyroid-medium radioiodide concentration ratio. In contrast, similar iodide pretreatment had no significant effect on fetal iodide transport. In all other respects, fetal iodide transport, although it was 10 times higher, did not differ significantly from maternal transport activity. Combined radiolabeled maternal (125I) and fetal (131I) rabbit thyroid tissue was eluted on Sephadex G-25 columns. Fractions were analyzed for both 125I and 131I activity, and the maternal to fetal ratios (125I/131I) were determined for each fraction. The majority of iodoproteins eluted with the void volume, and the 125I/131I ratio was constant in these fractions. Thereafter, two peaks of elevated 125I/131I activity could be observed. Peak A eluted below lysozyme (Mr = 14,300) and above insulin (Mr = 6,000), with an apparent mol wt of 8,000 to 10,000. A second peak, peak B, eluted from the column at a site similar to that of MIT or a protein of Mr of 2,000. Ascending paper chromatography of this latter peak of 125I/131I activity and MIT was carried out in two solvent systems. In both systems, peak B comigrated with MIT. These findings suggest that the failure of fetal thyroid tissue to exhibit autoregulation may be associated with the reduced iodination of a compound with an approximate Mr of 8,000 to 10,000. The role of this substance in iodide transport remains to be identified. The reason for the apparent increase in the labeling of MIT observed in maternal vs. fetal tissue is unknown.

Intrathyroidal thyroglobulin in streptozotocin-diabetic rats

In order to elucidate whether or not the 'coupling defect' observed in thyroids from diabetic rats is due to a structural defect of intrathyroidal thyroglobulin (Tg), the sedimentation pattern and the stability of the thyroidal soluble iodoproteins were studied in control (C), food restricted (FR), diabetic (D) and insulin-treated diabetic (D+I) rats fed a low iodine diet either with (NID) or without (LID) iodide supplementation and labelled with 125I: acutely, 24 h prior to sacrifice and chronically, by feeding the corresponding diet labelled for 60 days. Diabetes resulted in a decrease of thyroidal weight, an increase of both thyroidal 127I content and concentration and decreased plasma TSH, irrespective of the diet. Insulin treatment reversed these alterations. Food restriction led to an intermediate situation between C and D. The iodoamino acid distribution in the acutely labelled thyroidal soluble iodoproteins showed a significant increase in the percent of organified 125I found as iodotyrosines (MIT and DIT) and a decrease of that found as iodothyronines (T3 and T4) both in D and FR. However, in the isotopically equilibrated groups, no differences were found except in LID-D where a slight increase in DIT and a decrease in T3 was found as compared to the corresponding control. The sedimentation patterns of both acutely and chronically labelled thyroidal soluble iodoproteins from all experimental groups displayed two peaks. The main one, corresponding to Tg, had a slightly lower sedimentation coefficient than the 19 S internal marker run in parallel, while the second one, relatively small, formed probably by dissociation of the main Tg peak, sedimented more slowly (12- 14 S).(ABSTRACT TRUNCATED AT 250 WORDS)

Biological and immunological characteristics of 125I-4Tyr and -18Tyr Escherichia coli heat-stable enterotoxin species purified by high-performance liquid chromatography

A rapid procedure for the separation of Escherichia coli heat-stable enterotoxin iodination products is described. A two-step procedure using reverse-phase chromatography results in the separation of native, noniodinated heat-stable enterotoxins from several distinctly iodinated species which differ in their ability to bind to brush border receptors. Sequence analysis of the radioligands demonstrated mutually exclusive labeling at the 4Tyr and 18Tyr residues. These tracers have been immunologically and biologically characterized and have been shown to be antigenically similar but to differ in their toxicity for suckling mice. The radioligands separated by this procedure demonstrate stable behavior for a period of months.

Low molecular weight thyroglobulin leading to a goiter in a 12-year-old girl

We characterized the abnormal thyroglobulin (TG) in the thyroid and serum of a 12-yr-old girl with a large sporadic multinodular goiter first noted at age 4 yr. She developed normally and had no clinical evidence of hypothyroidism. However, her serum T4 was less than 1.0 microgram/dl, T3 was 125 ng/dl, and TSH was 155 microU/ml. Serum PBI was 9.7 micrograms/dl, and more than 90% was not extractable with butanol. The 24-h radioactive iodine uptake was 55%, not dischargeable by perchlorate. Hormone formation was tested by the administration of 131I before surgery. [131I]T4 and [131I]T3, but not 131I-labeled iodotyrosines, were present in the thyroidal venous blood. Hydrolysis of 10,000 X g supernatants from three randomly obtained samples of the goiter revealed 66-77% of the 131I as iodotyrosines, 2-4% as iodothyronines, and 10-12% as undigestable material; the MIT to DIT ratio ranged from 3.1-8.7, and the T4 to T3 ratio ranged from 2.3-8.3. The TG level was 2.5 mg/g in the goiter and 9.4 micrograms/ml in the serum. The RIA displacement curves for the goiter and serum TG levels were both identical to the curve produced by normal human TG. The iodine contents of goiter and serum TG were 0.49% and 0.47% (wt/wt), respectively. The T4 to T3 ratio was lower in the goiter (approximately 5) than in the serum iodoprotein (approximately 45), whereas the calculation of the T4 to T3 ratio in the thyroidal secretion was less than 1. The goiter and serum TG bound normally to Concanavalin A, indicating that they contained carbohydrate. When either serum- or goiter-soluble proteins were gel-filtered (Bio-Gel A-5m), TG immunoreactivity and stable iodine elution profiles were the same, suggesting that no significant amounts of other iodoproteins were present in the thyroid or circulation. Both serum and goiter TG elution volumes corresponded to mol wt of approximately 9 X 10(4). A sedimentation rate of 10-11 S was found for both goiter and serum TG. An abnormally low mol wt of 8.5-9.0 X 10(4) was determined by sodium dodecyl sulfate-electrophoresis, in good agreement with the estimates from gel filtration studies. A single band was present on sodium dodecyl sulfate-electrophoresis regardless of whether the TG was reduced before the analysis. Thus, it is very unlikely that the low molecular weight was due to partial hydrolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Dynamic nature of the association of large tumor antigen and p53 cellular protein with the surfaces of simian virus 40-transformed cells

A molecular complex of simian virus 40 large tumor antigen (T-Ag) and p53 cellular protein is present on the surface of simian virus 40-transformed mouse cells. The stability of the association of the two proteins with the cell surface was characterized. Cells were either surface iodinated by the lactoperoxidase technique or metabolically labeled with [35S]methionine, and surface antigens were detected by differential immunoprecipitation with specific antibodies immediately after labeling or after incubation at 37 degrees C. A rapid, concomitant disappearance of T-Ag and p53 from the cell surface was observed. The half-life of iodinated surface T-Ag was less than 30 min, whereas that of [35S]methionine-labeled surface T-Ag was 1 to 2 h. Although T-Ag and p53 were rapidly lost, both were also rapidly replaced on the cell surface, since newly exposed molecules could be detected when cells were reiodinated after a 2-h chase period. Control experiments established that the loss of the surface molecules was not induced by the iodination reaction. The appearance of surface T-Ag was prevented when cellular protein synthesis was inhibited with cycloheximide. The disappearance and replacement of T-Ag and p53 appeared to be energy-independent processes, as neither was inhibited by sodium azide or 2,4-dinitrophenol. Incubation of iodinated cells at 4 degrees C did block the loss of T-Ag and p53. These observations suggest that T-Ag and p53 are coordinately turned over in the plasma membrane. The nature of the association of the T-Ag-p53 complex with the cell surface can best be described as highly dynamic.

Some theoretical questions of mechanisms of thyroid hormone action

The effects of iodothyronines, the suggested mechanisms of their action, the methodical difficulties of determining receptors of thyroid hormones, the significance of iodothyronine formation during hormone action and some stereochemical aspects of the receptor--thyroid hormone interaction have been reviewed and a new model of the thyroid hormone action has been developed. It is suggested that the thyroid hormones may interact with more than one protein and nucleic acid at the same time and in this way "help" the interaction of macromolecules, thus catalysing and modulating biochemical processes of diverse character.

Thyroxine-rich iodopeptides as fragment of reduced guinea pig thyroglobulin

Full reduction of guinea pig thyroglobulin with mercaptoethanol followed by polyacrylamide gel electrophoresis reveals the presence besides the well known three polypeptide chains, of small amounts of iodopeptides with a molecular weight of 3 000 to 46 000 daltons. One of these peptides with a molecular weight of roughly 10 000 daltons has a much higher efficiency to couple iodotyrosines into thyroxine than any other fragment of thyroglobulin. Despite its small quantity this peptide contributes more than one third to the total thyroxine synthesis from a given iodide shot at any time up to five days after its injection. Iodopeptides akin to that found in guinea pigs were recently described by several authors in different species. They probably represent the preferential domains for hormone synthesis within the intact thyroglobulin molecule.

Most iodinatable fibroblast surface proteins accompany the cytoplast membrane during cytochalasin B-mediated enucleation of chick embryo fibroblasts

Six different proteins are found to be reproducibly exposed on the cell surface of chicken embryo fibroblasts (CEF) by the criterion of lactoperoxidase-catalyzed iodination (250,000, 185,000, 130,000, 100,000, 87,000, and 75,000 daltons). We wondered whether cell enucleation might lead to a differential partition of these surface proteins with the karyoplast or cytoplast membrane. We found that there is a marked enrichment of most iodinatable cell surface proteins in the cytoplast after cytochalasin-mediated enucleation of cell monolayers. Nearly all the iodinatable fibronectin remains with the cytoplast. Of the six labeled proteins, the karyoplast membrane contains a small amount of the 130 kdalton protein as well as trace levels of the 100-, 85-, and 75-kdalton proteins. Proteolysis or selective shedding of membrane proteins were not significant factors in the relative exclusion of iodinatable membrane proteins from the karyoplast. The cytoplast could replace some exposed membrane proteins after removal by trypsinization; however, fibronectin was not detectable within 10 h. That the karyoplast was not capable of membrane protein synthesis and/or insertion was suggested by the lack of any change in the labeling pattern of karyoplasts up to 8-h incubation after enucleation. A variety of control studies indicated that the surface proteins identified in this report were cell-derived and not adsorbed serum components. That some of the iodinatable proteins are intrinsic membrane proteins was suggested by their resistance to removal by conditions thought to extract extrinsic membrane proteins (i.e., low salt, high salt, and NaOH washes). lack of effect of cytoskeletal disrupting agents (preliminary evidence) suggests the nonrandom partition of membrane proteins may depend on anchoring of membrane proteins by a system(s) in the cytoplast other than intact microtubules and microfilaments.

A new mechanism for the reabsorption of thyroid iodoproteins: selective fluid pinocytosis

Rat thyroid hemilobes were incubated in presence of exogeneous, heterologous and homologous thyroglobulins. The median density of the thyroglobulin molecules originally added to the medium was compared with that of the molecules remaining at the end of a three-hour incubation period (37 degrees C). A certain degree of specificity in the reabsorption process of thyroglobulin was found: the uptake of homologous molecules (rat) was higher than heterologous (hog) molecules. The median density of the iodoproteins remaining after the incubation did not change for the heterologous whereas it shifted towards lower density for the homologous thyroglobulins (equilibrium labelled, 35 iodine atoms/molecule). In addition, rat follicular cells display selectivity in the endocytosis of homologous thyroglobulin. Among the rat molecules, the normally iodinated are taken up more actively than the lowly iodinated or newly synthesized ones. Dissimilarity in the median density of the thyroglobulin molecules before and after endocytosis was only evident for the equilibrium-labelled, normally iodinated rat preparation: the disappearance from the medium of 25-30% of exogenous iodoproteins was sufficient to lower significantly the median density of the remaining molecules. This means that the thyroglobulin molecules having higher density are taken up preferentially by the tissue. A mechanism involving specific interactions between the iodoproteins and the surface of thyroid cell is suggested.

Iodination of thyroglobulin. An intracellular or extracellular process?

The location in the thyroid follicle of the iodination of thyroglobulin has been a matter of debate for several decades. This problem is not a question of mere academic interest. Knowledge of the locus--or loci--of iodination is necessary for a full understanding of the mechanisms involved in thyroid-hormone synthesis and release. In the discussion about this problem 3 fundamentally different views have been--and still are--advocated. The first view implies that the site of iodination is the follicle lumen, the second that iodination is an intracellular process restricted to some organelle(s) in the follicle cells and the third that iodination occurs at the interface between the follicle cells and the follicle lumen. Below I will survey the major observations on which these different opinions are based and discuss the validity of the interpretations.

A kinetic model of human thyroid hormones and their conversion products

We have examined the in vivo distribution and metabolism of radiolabeled T4 and T3 in 14 normal subjects using a kinetic model. Tracer amounts of [131I]T4 and [125I]T3 were injected simultaneously, and plasma samples were obtained for up to 7 days thereafter. Separation of these samples by thin layer chromatography yielded kinetic curves for 131I- and 125I-labeled T4, T3, iodide, and iodoprotein, which were then used to develop a kinetic model. The model includes several features. 1) Submodels were developed for T4, T3, iodide, and iodoprotein which simultaneously fit the observed data. 2) Two other submodels were needed for data fit, the first representing rT3, the other representing other intermediates, including the various diiodothyronines. The latter submodel was patterned initially after 3,3'-diiodothyronine kinetics. It was required to account for the delay in appearance of labeled iodide produced from the degradation of T4, and rT3 and proved to be essential for the successful fit of the data. 3) The model accounts for the conversion of T4 to T3 and rT3. Even though rT3 is quantitatively significant as a degradation pathway for T4, its presence does not contribute significantly to total plasma radioactivity after T4 administration because of its rapid turnover in comparison with T4. 4) The small amount of iodoprotein formed is a major contributor to total plasma radioactivity within 3 days after T3 administration. 5) The model permits the elimination of two methodological errors: that due to the presence of labeled iodide, T3, or T4 contaminants in the administered labeled hormones, and that due to the small amount of cross-over between thin layer chromatography peaks. The model provides a concise description of our current understanding of thyroid hormone metabolism and suggests areas where further information is required.

Degradation of proteins microinjected into IMR-90 human diploid fibroblasts

Erythrocyte ghosts loaded with 125I-labeled proteins were fused with confluent monolayers of IMR-90 fibroblasts using polyethylene glycol. Erythrocyte-mediated microinjection of 125I-proteins did not seriously perturb the metabolism of the recipient fibroblasts as assessed by measurements of rates of protein synthesis, rates of protein degradation, or rates of cellular growth after addition of fresh serum. A mixture of cytosolic proteins was degraded after microinjection according to expected characteristics established for catabolism of endogenous cytosolic proteins. Furthermore, withdrawal of serum, insulin, fibroblast growth factor, and dexamethasone from the culture medium increased the degradative rates of microinjected cytosolic proteins, and catabolism of long-lived proteins was preferentially enhanced with little or no effect on degradation of short-lived proteins. Six specific polypeptides were degraded after microinjection with markedly different half-lives ranging from 20 to 320 h. Degradative rates of certain purified proteins (but not others) were also increased in the absence of serum, insulin, fibroblast growth factor, and dexamethasone. The results suggest that erythrocyte-mediated microinjection is a valid approach for analysis of intracellular protein degradation. However, one potential limitation is that some microinjected proteins are structurally altered by the procedures required for labeling proteins to high specific radioactivities. Of the four purified proteins examined in this regard, only ribonuclease A consistently showed unaltered enzymatic activity and unaltered susceptibility to proteolytic attack in vitro after iodination.

Identification of an intracellular pathway of thyroxine synthesis by dispersed thyroid cells

This study deals with the identification of the biochemical events involved in the metabolic sequence leading from the synthesis to the release of thyroxine in the dispersed thyroid cell system. (1) Using an experimental model allowing the differentiation between intracellular and extracellular sites of iodination, it is shown that thyroxine is synthesized inside the cells by an iodinating system sensitive to thyrotropin stimulation. (2) The secretion of thyroxine synthesized inside the cells is not mediated by an exocytotic-endocytotic phenomenon. Colchicine, vinblastine, fluoride, propanolol and chlorpromazine, at concentrations equal to or 10--100-times higher than those required to inhibit hormone release in follicular-organized thyroid tissue have no effect on thyrotropin-stimulated thyroxine secretion. (3) The secretion involves the intracellular proteolysis of hormone-containing iodoprotein(s) which, in addition to free thyroxine, generates free mono- and diiodotyrosines. Free thyroxine is released into the incubation medium and iodotyrosines are deiodinated under normal conditions and accumulate in the presence of an inhibitor of iodotyrosine deiodinase: 3,5-dinitrotyrosine. This proteolysis is inhibited by 5 mM chlorpromazine. These data indicate that the complete metabolic sequence leading from the uptake of iodide to the release of free thyroxine into the incubation medium can be described as an 'intracellular metabolic sequence for thyroxine synthesis'.

Effect of epinephrine and 5-hydroxytryptamine on in vitro thyroid iodine organification

The effect of epinephrine (E) and 5-hydroxy-tryptamine (5-HT) on some elements involved in thyroid iodine organification was studied using a bovine thyroid subcellular fraction sedimented at 30 000 g. 131I-incorporation into particulate proteins and into tyrosine ws increased by 10(-3) M and 10(-5) M E and 5-HT. This effect was inhibited by 6-n-propyl-2-thiouracil and by catalase. In the presence of these amines the activity of NADPH-cytochrome c reductase was not modified. Both E and 5-HT were able to generate H2O2 when added to the particulate fraction as measured by the oxidation of o-dianisidine. H2O2 generation and [131I]iodotyrosine formation were inhibited by pargyline, a monoamine oxidase (MAO) inhibitor. Tyramine, a specific substrate for thyroid MAO, produced H2O2 and increased [131]iodotyrosine formation. This effect was higher when compared to the effect elicited by E or 5-HT. The stimulatory effects of tyramine were blocked by pargyline. The action of tyramine on H2O2 generation and [131I]iodotyrosine formation was diminished when E or 5-HT were incorporated to the system. From these results it suggested that E and 5-HT serving as MAO substrates would generate H2O2 and in this way increase the thyroid iodine organification. On the other hand, these amines would be able to reduce the increased H2O2 generation induced by tyramine and thus decrease the iodination process. These findings could explain the stimulatory or inhibitory effects of biogenic amines on thyroid function which are dependent on the previous thyroid activity.

Proteins iodinated by the chloramine-T method appear to be degraded at an abnormally rapid rate after endocytosis

Proteins labeled with either (3)H by reductive methylation or (125)I by the chloramine-T method were incubated with Xenopus laevis oocytes; the incorporation and acid precipitability of the proteins were then studied. The uptake rates of both specifically incorporated (vitellogenin) and nonspecifically incorporated proteins (bovine serum albumin and X. laevis serum proteins lacking albumin) were not influenced by the method of labeling. However, (125)I-labeled proteins were apparently degraded at rates far exceeding their (3)H-labeled counterparts, based on the generation of acid-soluble radioactivity. Thus, after a 3-hr incubation, 3-5 times more (125)I-labeled bovine serum albumin and X. laevis serum proteins lacking albumin were degraded than the corresponding (3)H-labeled proteins (95% compared to 30% and 75% compared to 15%, respectively), whereas after a 24-hr incubation, the degradation of (125)I-labeled vitellogenin was 15 times greater than that of [(3)H]vitellogenin labeled in vivo (60% compared to 4%). Moreover, examination of the relative amounts of (3)H- compared to (125)I-labeled bovine serum albumin deposited into the exogenously derived yolk platelet compartment of the oocyte revealed 7 times more acid-precipitable (3)H-labeled protein, indicating that the observed discrepancies were not due to reincorporation of the (3)H-labeled ligands. Passage of dissolved oocytes previously exposed to (125)I-labeled bovine serum albumin (chloramine-T method) over a column of Bio-Gel P-10 revealed some breakdown of bovine serum albumin to intermediate molecular weight components and the presence of a large amount ( approximately 90%) of labeled low molecular weight compounds, which analysis showed to be 72% free iodine. The evolution of either iodotyrosine or free iodine would nevertheless be perceived as protein degradation by most analytical procedures (e.g., acid precipitation or autoradiography). We conclude, therefore, that apparent degradation rates observed for endocytotically incorporated proteins may vary depending on the method used to label the protein and caution should be exercised when interpreting results obtained with labeled, particularly chloramine-T labeled, proteins.

Binding of sea anemone toxin to receptor sites associated with gating system of sodium channel in synaptic nerve endings in vitro

Iodination of toxin II from the sea anemone Anemonia sulcata gives a labeled monoiododerivative that retains 80% of the original neurotoxicity. This derivative binds specifically to rat brain synaptosomes at 20 degrees C and pH 7.4 with a second-order rate constant of association ka = 4.6 x 10(4) M-1 sec-1 and a first-order rate constant of dissociation kd = 1.1 x 10(-2) sec-1. The binding occurs on the Na+ channel at a binding site distinct from that of other gating system toxins like batrachotoxin, veratridine, grayanotoxin, aconitine, and pyrethroids. The maximal binding capacity Bmax is 3.2 pmol/mg of protein (i.e., about two sea anemone toxin binding sites per tetrodotoxin binding site) and the Kd is 240 nM for the monoiododerivative and 150 nM for the native toxin. Corresponding binding parameters for the association of a 125I-labeled derivative of toxin II from the scorpion Androctonus australis Hector are Bmax = 0.3 pmol/mg of protein and Kd = 1 nM, whereas the Kd of the unmodified scorpion toxin is 0.6 nM. Competition experiments involving scorpion toxins, sea anemone toxins, and synaptosomes demonstrate that, although the sea anemone toxin is able to displace the scorpion toxin bound to synaptosomes, the scorpion toxin does not displace the sea anemone toxin. The sea anemone toxin but not the scorpion toxin binds to depolarized synaptosomes. Differences between binding properties of the two polypeptide toxins are analyzed in the discussion.

The role of calcium and guanosine 3':5'-monophosphate in the action of acetylcholine on thyroid metabolism

The role of calcium and guanosine 3':5'-monophosphate (cyclic GMP) in the regulation of thyroid metabolism has been investigated in dog thyroid slices. Carbamoylcholine enhanced glucose carbon-1 oxidation, protein iodination, cyclic GMP accumulation and decreased thyrotropin-induced adenosine 3':5'-monophosphate (cyclic AMP) accumulation and iodine secretion; it did not affect protein synthesis. The effects of carbamoylcholine were reproduced under various experimental conditions by supplementary calcium in the medium, ouabain, and in media in which Na+ had been replaced by choline chloride. They were inhibited by lanthanum. These results further support the hypothesis that free intracellular Ca2+ is the intracellular signal for carbamoylcholine effects and suggest that a Na+ -gradient-driven Ca2+ extrusion mechanism operates in the thyroid cell. Mn2+ reproduced the effect of Ca2+ on glucose oxidation, protein iodination and cyclic GMP accumulation in Ca2+ -depleted slices and medium, and thus mimicked some intracellular effects of Ca2+. On the other hand Mn2+ inhibited the carbamoylcholine effect on thyrotropin-induced thyroid secretion and cyclic AMP accumulation, and Ca2+ inhibited the Mn2+-induced cyclic GMP accumulation. This suggests that the two ions compete for the same channel. Similarly Mn2+ inhibited calcium effects in the presence of ionophore A23187. Procaine inhibited protein iodination under all conditions suggesting a primary effect; it also inhibited all carbamoylcholine and ouabain actions. However the drug did not inhibit the effects of choline chloride and its action was reversed by raising carbamoylcholine but not Ca2+ concentration; it is therefore doubtful that procaine acts by blocking Ca2+ channels. In media without added Ca2+, Mn2+ increased cyclic GMP accumulation but did not decrease thyrotropin-induced cyclic AMP accumulation or iodine secretion, which suggests that cyclic GMP cannot be the sole mediator of the latter two effects of carbamoylcholine.

Imparied cyclic-AMP response to thyrotrophin in congenital hypothyroidism with thyroglobulin deficiency

A 19 year old man had congenital hypothyroidism and severely retarded development. His thyroid gland was not enlarged and laboratory findings included low serum concentration of T4 (2.8 microgram/100 ml) and T3 (16 ng/100 ml) with a high level of TSH (52 microU/ml) that rose to 192 microU/ml after TRH. 131I uptake by the thyroid was normal (41.5% at 24 h) and did not show a normal increase after exogenous TSH administration (49.5% at 24 h). The perchlorate discharge test was negative and no antibodies against thyroid antigens were found. Studies on the biopsy specimen revealed low iodide trapping by the thyroid slices and no formation of cyclic AMP after TSH was added to the medium. The endogenous TSH of the patient was biologically active increasing cyclic adenosine monophosphate c-AMP concentration in normal thyroid slices. No thyroglobulin was found in the thyroid tissue either by immunological or ultracentrifugational methods. An increased proportion of iodoalbumin was present in the serum. We postulate that the fundamental defect in this gland is an impaired generation of c-AMP by the defective thyroid cell and deficiency of thyroglobulin formation resulting in inadequate thyroxine and triiodothyronine synthesis.

Topological organization of proteins in an intracellular secretory organelle: the synaptic vesicle

Intact synaptic vesicles prepared from the electric organ of the marine elasmobranch Narcine brasiliensis have eight major polypeptides demonstrable on sodium dodecyl sulfate gels. Six of these copurify with the synaptic vesicles during isolation of vesicles by chromatography on CPG-3000 and, by this criterion, are specific to vesicles. The other two are either shared by many membrane or are contaminants. One of these proteins comigrates with actin. Three different approaches were used to determine which proteins were exposed on the external, cytoplasmic surface of the vesicle and which were internal. The first was susceptibility to the proteases trypsin, Streptomyces griseus protease, and Pronase; the second was labeling by the membrane-impermeable reagent diazotized [125I]iodosulfanilic acid; and the third was iodination catalyzed by lactoperoxidase. In general, the three approaches give the same result: six of the eight proteins are on the external, cytoplasmic surface and two are accessible only after the vesicles are lysed by freezing and thawing or by detergents. Five of the vesicle-specific proteins are external and one is internal. The actin-like protein is internal. Proteins involved in the interaction of vesicles with the presynaptic membrane during exocytosis might be expected to be vesicle specific and external.

Depletion of colloid 27S and larger thyroid iodoproteins following treatment with propylthiouracil

By means of a micropuncture technique and microgel electrophoresis the luminal content of single rat thyroid follicles were analyzed during PTU treatment for 4 weeks. The relative amount of aggregates of thyroglobulin (i.e. the 27S iodoprotein and larger complex) was reduced from 15 per cent to approximately 3 per cent after 48 h. The aggregates were practically absent after 2 weeks. The thyroglobulin fraction was the predominant colloid constituent. The protein concentration of the colloid was not changed at the end of the period of PTU treatment (8.9 g/100 ml). It is concluded that PTU inhibits the aggregation of thyroglobulin to a larger complex. The results further indicate that the aggregates of thyroglobulin are preferentially localized to the periphery of the lumen in the larger follicles.

Bromodeoxyuridine-induced reversion of transformed characteristics in BHK21 cells: changes at the plasma membrane level

When BHK21 cells transformed by hamster sarcoma virus are grown in the presence of 5-Bromedeoxyuridine (BUdr), several in vitro properties of the transformed cells such as morphology, adhesiveness, and alignment, revert towards a state close to that of untransformed cells. We have studied plasma membrane changes associated with this phenotypic reversion by several different biochemical methods. Reversion is accompanied by a reappearance of Fibronectin, an increase in a membrane-associated protein of M.W. 100,000 which is increased in transformed cells and a decrease in Con A-agglutinability. On the other hand, several membrane changes associated with malignant transformation namely, the increase in an integral membrane protein M.W. 177,000, the higher rate of hexose uptake, the increase in high molecular weight surface glycopeptides and, to some extent, the increase in the density of intramembranous particles, did not revert under BUdr treatment. Thus, membrane properties of transformed cells may be dissociated into two main groups by BUdr treatment. In addition, the exposure and glycosylation of a growth-regulated membrane protein M.W. 160,000 was highly sensitive to BUdr.

Degradation of proteins microinjected into cultured mammalian cells

Iodinated proteins were degraded after injection into HeLa cells at first-order rates with half-lives varying from three hours for the trout monhistone chromosomal protein, HMG-T, -to 60 hours for whale myoglobin. Fluoresceinated-bovine serum albumin (fl-BSA) was degraded almost twice as fast as unmodified BSA. The rate of degradation of 125I-BSA was very similar in eight cell lines of mouse, human, monkey and rat origin. Microinjected proteins were analyzed on SDS-acrylamide gels after injection, and for BSA and immunoglobin G, all remaining intracellular 125I migrated at the molecular weight of the injected proteins. By contrasting, more than 80% of the extracellular 125I chromatographed as iodotyrosine. With the exception of fl-BSA, which exhibited perinuclear accumulation in approximately one-half of the injected cells, autoradiography showed that throughout the period of study the injected proteins remained dispersed in the cytoplasm.

Influence of magnesium and polyamines on the reactivity of individual ribosomal subunit proteins to lactoperoxidase-catalyzed iodination

30S and 50S subunits, in the presence of either 20 mM Mg2+ or 6 mM Mg2+ and 5mM spermidine plus 25 mM putrescine, were observed to completely associate to form 70S monosomes as monitored by sucrose gradient sedimentation. Subunits maintained under the above ionic conditions were compared with 30S and 50S particles at low (6 mM) magnesium concentration with respect to the reactivity of individual ribosomal proteins to lactoperoxidase-catalyzed iodination. Altered reactivity to enzymatic iodination of ribosomal proteins S4, S9, S10, S14, S17, S19, and S20 in the small subunit of ribosomal proteins, L2, L9, L11, L27, and L30 in the large subunit following incubation with high magnesium or magnesium and polyamines suggests that a conformation change in both subunits accompanies the formation of 70S monosomes. The results further demonstrate that the effect of Mg2+ on subunit conformation is mimicked when polyamines are substituted for magnesium necessary for subunit association.

Direct effects of trypan blue on thyroid secretion

Trypan blue directly inhibited in vitro thyroid secretion (butanol soluble 125I release to the media) induced by both thyroid stimulating hormone (TSH) and dibutyryl cAMP. Intracellular colloid droplet counts were also decreased. Inhibition was directly proportional to dye concentration and could be overcome by supramaximal TSH and dibutyryl cAMP. Inhibition could be observed as early as 20 min of incubation, was not increased by preincubation, and could even be demonstrated after TSH in vivo. Trypan blue, in vivo, produced similar inhibition of thyroid secretion. Incubation of 125I-thyroglobulin with lysosomal enzymes revealed inhibition with much lower concentrations of dye. Inhibition of lysosomal enzyme(s) would not appear to explain the marked decreases in colloid droplets, and this may represent two separate effects of trypan blue on thyroid secretion.

[Effects of the length of radioiodine treatment of hyperthyroidism on the distribution of blood levels of calcium and phosphorus as a function of sex and age]

An evaluation was made of the incidence of hypoparathyroidism after 131I management of hyperthyroidism and of the effect of irradiation on the relation between blood calcium, phosphorus and proteins and age in normal subjects. 356 treated patients and 216 controls were examined. Serum calcium was determined from 2 to 6 yr after treatment. It was found that calcium values decrease with age in males, wherease in women this phenomenon is less marked and, indeed, is no longer apparent over the age of 30. In the normal male, phosphrous also decreases with age, while in females there is a fall until the age of 30-40 yr, followed by a rise. Only 1 subject with a value of 8.45 mg calcium/100 ml was noted in the treated group and there was no significant difference between the means for the two groups, suggesting that parathyroid insufficiency is a virtually non-existent complication of the 131I treatment of hyperthyroidism. The relation between blood calcium and phosphorus and age in the treated group was examined with reference to subjects with normal thyroid function only. In the case of calcium, values were no longer related to age after treatment in males, while phosphorus values fell to below those observed in females, coupled with an increase in function of age as in women, though this itself was not statistically significant. Treatment also suppressed the relation between total blood proteins and age noted in the normal male. None of the parameters considered displayed any significant changes in the treated females. It would thus seem that 131I abolishes the differences in blood calcium and phosphorus mean values and age-linked patterns normally found between males and females.

Euthyroidism via iodide supplementation in hereditary congenital goiter with thyroglobulin deficiency

We have studied hereditary congenital goiter in an inbred strain of goats. On a normal diet, the goats were hypothyroid and iodide taken up by the gland was released rapidly in the form of iodinated macromolecular material. This resulted in a low thyroidal iodine pool. An extremely low amount of thyroglobulin-related antigens (12 microgram/g tissue; normal, 100 mg/g tissue) was detected in the goitrous gland by RIA. Addition of 1 mg I-/day to the diet made the goats euthyroid and the serum protein-bound iodine increased to high values. Even under these conditions, however, the amount of thyroglobulin-related antigens was not significantly elevated (19 microgram/g tissue). On sucrose gradient, these antigens sedimented in the 7S region. No thyroglobulin-related antigens sedimented at 12S or 19S. Besides iodoalbumin, a heterogeneous group of abnormal iodoproteins containing T3 and T4 was observed with this high iodide intake and may have accounted for the hormone production. The abnormal iodoproteins had a molecular weight of 300,000-500,000 and a sedimentation value of about 7S. From these findings, we conclude that these goats were unable to synthesize thyroglobulin but with excess iodide, there was sufficient formation of T3 and T4 in the abnormal iodoproteins to make the animals euthyroid.

Thyrotropin binding to cultured lymphocytes and thyroid cells

The TSH-binding properties of human lymphocytes in continuous culture were studied and compared to those of bovine and human thyroid cells in primary culture. Both lymphocytes and thyroid cells had maximal TSH-binding capacity at pH 5.2. At pH 7.4, thyroid cells bound 15% but lymphocytes bound only 3% of the amount bound at pH 5.2. At 37 C, maximal binding of [125I]iodo-TSH to lymphocytes was reached within 60--90 min and maximal binding to thyroid cells was reached within 15--20 min. TSH binding to lymphocytes was salt sensitive, being inhibited to 50% by 0.2 mM MgCl and 0.4 mM CaCl2 and by 20 mM Kl, KCl, and NaCl. The saturable binding of bovine TSH (bTSH) to thyroid cells at pHs 5.2 and 7.4 was above 90% of the total binding. Saturable binding of bovine TSH (bTSH) to thyroid cells at pHs 5.2 and 7.4 was above 90% of the total binding. Saturable binding to lymphocytes at pH 5.2 was also above 90%, but at pH 7.4 was 75% of total. At pH 5.2, both cell types displayed identical displacement curves of [125I]iodo-bTSH by unlabeled bTSH. Pure hCG, human placental lactogen, human GH, and insulin cross-reacted to less than 1% with [125I]iodo-bTSH binding to lymphocytes at pH 5.2, whereas a crude preparation of hCG and human FSH plus human LH showed a strong cross-reaction. Nonhormone glycoproteins, including mucin, normal human gamma-globulin, and bovine thyroglobulin showed intermediate cross-reactivity. At pH 7.4, the cross-reactivity of normal human gamma-globulin, bovine thyroglobulin, and pure hCG with bTSH binding to both lymphocytes and thyroid cells was below 1%. The TSH-binding properties of lymphocytes and thyroid cells show many similarities but differ in kinetics and the relative binding capacity at neutral pH. Although the physiological significance of these differences is not yet clear, cultured cells provide a convenient system for studies of TSH-receptor interaction.

Specific binding of iodinated growth hormone to rat liver in vivo

The specific uptake by rat liver of human (hGH) and bovine (bGH) GHs labeled with 125I was studied by an in vivo procedure. A significant reduction of the uptake was observed when labeled hormones were injected together with different amounts of the corresponding native GH. This reduction was dose dependent, and the concentration of native hormone that prevents 50% of the liver uptake of the labeled hormone was close to 12 microgram/100 g BW. In normal rats, only native hGH or bGH significantly decreased the liver uptake of [125I]iodo-bGH, while bovine PRL (oPRL) or heat-denatured bGH were inactive. The highest inhibition of the uptake of [125I]iodo-hGH by rat liver was obtained when this labeled hormone was injected either together with hGH or with bGH plus oPRL while partial displacement was observed with bGH or oPRL. These data suggest that hGH binds to both somatotropic and lactogenic sites in the liver of normal rats. In hypophysectomized animals, only the somatogenic binding sites could be detected.

Change of the protein composition of the thyroid colloid during treatment with propylthiouracil and thyroxine: a microgel electrophoretic study of single rat thyroid follicles

Prophylthiouracil and thyroxine were given daily to rats for 4 weeks. Samples of colloid were collected in vivo from the superficial thyroid follicles during this period and their protein composition was analysed by gel electrophoresis. It was observed that the aggregates of thyroglobulin, i.e., the 27-S thyroid iodoprotein and the heavier fractions, were reduced to 50% after 1 week and were almost absent after 2 weeks. A faster migrating thyroglobulin fraction was observed in the samples of colloid and in the homogenate of the whole gland after 48 h of treatment. During the following period of treatment there was an increase in the relative amount of the faster migrating thyroglobulin fraction compared to 19-S thyroglobulin in the colloid, the former comprising approx. 75% of the globulins after 4 weeks, It can be concluded that propylthiouracil inhibits the formation of the 27-S iodoprotein and that a structurally altered and iodine-poor thyroglobulin fraction is accumulated in the follicle lumen.

Some disturbances related to iodination and utilisation of thyroglobulin and 27 S iodoprotein in non-toxic multinodular goitre

The relationships among the thyroid iodoproteins, their biosynthesis in vitro in thyroid slices and the histological structure of a multinodular, sporadic goitre was examined after strumectomy from a euthyroid 51-year-old woman. Using sedimentation methods 27S, thyroglobulin (TG), 12S and 3--8S proteins were found. Besides these, 4 to 5 other proteins with molecular weights between 165,000 and 36,000 daltons were detected by polyacrylamide gel electrophoresis. The concentration of soluble proteins was very low (3 mg/100 mg wet tissue), particularly TG (0.69 MG/100 MG). The sedimentation constant (18.3S) of goitrous TG was lower than mature 19S-TG and it was poorly iodinated (0.06% w/w). 27S iodoprotein was present in the goitre extract. Thyroid slices of goitre tissue incorporated 14C-leucine into proteins and synthesized TG and its subunits. Newly synthesized proteins were rapidly released from the microsomes. Pathohistologically, struma colloido-microfolliculare with dystrophic-proliferative changes was noted. In the large follicles which were filled with colloid, dystrophic alterations in thyrocytes and desquamation of the follicular epithelium were observed. In conclusion, it is suggested that the presence of poorly iodinated, immature TG in nontoxic multinodular, sporadic goitre, in the absence of iodine deficiency, probably results in disturbances in the utilization of TG from the follicular lumen. In the follicular lumen under these conditions it is possible that 27S protein is formed from pre-existing poorly iodinated TG. These findings suggest that inability to resorb colloid may be a cause of nodule formation.

Afrikander cattle congenital goiter: characteristics of its morphology and iodoprotein pattern

The morphology and some properties of the complex iodoprotein pattern of the genetically determined congenital goiter in Afrikander cattle is described. The goiter contained irregularly shaped follicles which were devoid of colloid and the follicular epithelial cells were elongated, measuring about 20 micrometer in length compared to 10 micrometer for normal thyroid cells. The goiter cells contained apical clusters of larger and more numerous lysosomes than normal thyroid cells. Apical vesicles containing electron-dense material which were in contact with the plasma membrane could be seen in most normal thyroid cells, but were extremely scarce in the goiter. In 36 cell profiles studied none was found. The endoplasmic reticulum cisternae of the goiter differed significantly from normal thyroid cells. Fewer ribosomes were seen to be attached to the membranes of goiter cells. Furthermore, unlike normal thyroid cells, many free polysomes were seen in goiter cells. The characteristics of the unusual iodoprotein pattern of the goiter extract, resolved by gel chromatography and sucrose density gradient centrifugation, were qualitatively and quantitatively similar to that described previously (Endocrinology 91, 470, 1972). A relatively small amount of the total soluble protein was iodinated. Of these, only a 12S sedimenting species was precipitated by antithyroglobulin immunoglobulin. When separated on polyacrylamide gels containing sodium dodecyl sulfate and mercaptoethanol, this 12S species was resolved into at least 14 polypeptide components ranging in molecular weights from less than 66,000--330,000. Three of the bands, representing a small percentage of the total protein, seemed to comigrate with the major polypeptides of thyroglobulin and were also precipitated with rabbit antihyroglobulin immunoglobulin. The data indicate that glycosylation of iodoproteins was not affected although 19S thyroglobulin synthesis and subsequent storage were drastically impaired.