Enkephalinase inhibitors potentiate substance P-induced secretion of 35SO4-macromolecules from ferret trachea

To study the roles of substance P (SP) and endogenous peptidases in regulating mucus secretion from ferret trachea, we measured the SP-induced release of 35SO4-labeled macromolecules after incubating segments of trachea in Ussing chambers in the presence and absence of selected inhibitors of proteolytic enzymes. Our strategy was based on the idea that if endogenous peptidases degrade SP, then inhibitors of these enzymes should potentiate SP-induced secretion. We found that tracheas of ferrets contained SP-like immunoreactivity, and that SP stimulated the release of bound 35SO4 with rapid onset and offset. Eighty-five percent of the total macromolecular radioactivity released was contained in fractions of molecular weights greater than 10(6). The response to SP was concentration-dependent and reproducible. Thiorphan potentiated the secretory response to SP in a concentration-dependent fashion and phosphoramidon potentiated SP-induced secretion, whereas other inhibitors of proteinases and peptidases were without effects. These results suggest that substance P may regulate mucus secretion in ferrets, and that enkephalinase (dipeptidyl carboxypeptidase II, EC 3.4.24.11) in the airway degrades SP in a physiologically significant fashion, and thereby regulates peptide-induced secretion.

Comparison of insulin-like growth factor I receptor and insulin receptor purified from human placental membranes

Insulin-like growth factor (IGF)-I receptor purified from human placental membranes as previously described (LeBon, T. R., Jacobs, S., Cuatrecasas, P., Kathuria, S., and Fujita-Yamaguchi, Y. (1986) J. Biol. Chem. 261, 7685-7689) was characterized. The IGF-I receptor was similar to the insulin receptor with respect to subunit structure (beta-alpha-alpha-beta), apparent sizes of deglycosylated alpha (Mr = approximately 88,000) and beta (Mr = approximately 67,000) subunits, and amino acid composition of the subunits. Monoclonal antibody specific to each receptor recognized its own receptor whereas polyclonal anti-human insulin receptor antibody cross-reacted with the IGF-I receptor, indicating that the receptors share one or more antigenic sites. Further characterization of the purified IGF-I receptor tyrosine-protein kinase activity indicated that by analogy with the insulin receptor the monomeric alpha beta form of the IGF-I receptor appears to have higher kinase activity than the intact receptor in the alpha 2 beta 2 form. The most significant difference between the two receptors was found in the N-terminal amino acid sequences of their alpha subunits, which apparently show 60% identity. The IGF-I receptor alpha subunit lacks residues corresponding to the N-terminal 4 amino acids of the insulin receptor alpha subunit. These results provide the first direct proof that the IGF-I receptor is a molecule distinct from the insulin receptor despite numerous similarities.

Differential effects of aging on adrenocorticotropin receptors, adenosine 3'5'-monophosphate response, and corticosterone secretion in adrenocortical cells from Sprague-Dawley rats

This study examined the effect of aging on adrenal cell function in Sprague-Dawley rats, as judged by the binding of iodinated Phe2, Nle4-ACTH-(1-38) to the adrenal cells, and the ability of the cells to respond to ACTH stimulation by the production of cAMP and corticosterone in vitro. Collagenase-dispersed adrenal cells obtained from 2-, 12-, and 18-month-old-rats were used. The maximum corticosterone concentration after incubation with ACTH was significantly lower (P less than 0.001) in the 12-month-old (40 +/- 7 ng/micrograms DNA) and 18-month-old rats (28 +/- 3 ng/micrograms DNA) compared to that in 2-month-old controls (102 +/- 9 ng/micrograms DNA). The ED50 values of ACTH-induced corticosterone production measured in the cell suspension were similar in 2- and 12-month-old groups (30 pg/ml), and the diminished production of corticosterone in the 12-and 18-month-old rats persisted after incubation with N6,O2-dibutyryl cAMP. Neither the number nor the binding affinity of adrenal receptors for [125I]I-Tyr23,Phe2,Nle4-ACTH-(1-38) changed from 2-12 months of age. Furthermore, increases in concentrations of intra- and extracellular cAMP after ACTH stimulation were not significantly different in the 2-, 12-, and 18-month-old groups. Similarly, adrenal hydrolysis of cAMP by low and high Km phosphodiesterases did not change significantly with advancing age. These results provide strong evidence that there is a diminished capacity for corticosterone production with aging in the rat, and that the site of the defect lies distal to binding of trophic hormone to its receptor and to the production of its secondary messenger. Finally, an age-related decline in adrenal steroidogenic capacity could be viewed as a counterregulatory mechanism invoked in old rats to compensate, at least partially, for elevated plasma ACTH and corticosterone concentrations.

Differential sensitivity of two functions of the insulin receptor to the associated proteolysis: kinase action and hormone binding

Since we observed that after purification the receptor kinase activity is rapidly lost under conditions where insulin binding function seems to be preserved, we have studied the cause(s) of receptor kinase inactivation. Highly purified placental insulin receptor preparations were analyzed by NaDodSO4/PAGE followed by silver staining or immunostaining using domain-specific antibodies raised against synthetic peptides corresponding to the amino acid sequences of the beta subunit. These studies revealed the intact 90-kDa beta subunit is degraded first to an 88-kDa form and then to a 50-kDa beta 1-subunit form by proteolysis even after purification when stored at 4 degrees C. The 88-kDa beta subunit, which lacks the carboxyl-terminal approximately equal to 2-kDa portion exhibits almost no autophosphorylation activity, nor does insulin stimulate autophosphorylation. The loss of kinase activity as measured by phosphorylation of the src-related peptide is correlated with the loss of the intact 90-kDa beta subunit. Degradation of the beta subunit to the 50-kDa form seems to be facilitated by the removal of the approximately equal to 2-kDa peptide. Present studies thus suggest that only the intact form of the beta subunit has full kinase activity in an insulin-dependent manner and that other forms, such as the 88-kDa beta subunit show little kinase activity. The inactivation appears to arise from a conformational change of the 90-kDa form, which makes it susceptible to proteolysis at the carboxyl-terminal end. These results imply that the carboxyl-terminal of the beta subunit is important for the manifestation of the tyrosine kinase activity of the insulin receptor.

Purification of rat adrenocortical actin and its use in an immunoprecipitation assay to quantitate cellular actin

In an earlier study on the long-term effects of the pituitary hormone corticotropin (adrenocorticotropin, ACTH), we reported that ACTH promotes the loss of 20-25% of the total actin in isolated rat adrenocortical cells. In a continuation of this work, we report here the purification to near homogeneity of rat adrenal actin. We demonstrate that the protein purified is adrenal actin, and use this actin in the DNAase immunoprecipitation assay of Snabes et al. to confirm our earlier observation of the effect of ACTH on adrenocortical actin. Finally, we describe several changes made in the original protocol of this immunoassay which we believe significantly improve the accuracy of the assay in estimating actin contents in tissue and cell samples.

The avian beta-adrenergic receptor: primary structure and membrane topology

Partial amino acid sequence information allowed the isolation of cDNA clones encoding the turkey erythrocyte beta-adrenergic receptor. Antisera raised against synthetic peptides encoded by the cDNA crossreacted with the purified receptor and appropriate tryptic fragments, confirming the identity of the cDNA. The receptor is composed of 483 amino acids and has a molecular mass of 54 kDa. Its sequence suggests that it is arranged predominantly in seven membrane-spanning sequences and a long cytoplasmic carboxyl-terminal domain. The extracellular amino-terminal domain contains a consensus sequence for N-glycosylation. The beta-adrenergic receptor displays overall structural similarity and weak sequence homology with rhodopsin. Because both proteins act by regulating GTP-binding proteins, a compact structure based on seven membrane-spanning regions may be a general model for receptors that act on G proteins.

Characterization of corticotropin receptors in human adrenocortical cells

[125I-Tyr23,Phe2,Nle4]ACTH-(1-38) ([125I]ACTH analog), which is equipotent with ACTH, was used to characterize ACTH receptors in human adrenocortical cells. Adrenals were obtained from brain-dead patients at the time of renal harvest with permission. Binding of [125I]ACTH analog to human adrenocortical cells was highly specific, rapid, reversible, and saturable. Analysis of the inhibition of binding of [125I]ACTH analog by ACTH was compatible with a single class of binding sites with an apparent dissociation constant (Kd) of 1.6 nM and a mean binding capacity of 3560 sites/cell. Concentration-response curves for cAMP and cortisol production were shifted to the left of the binding curve, with ACTH concentrations required for half-maximal stimulation being 20- and 720-fold less, respectively, than those for binding. Extracellular calcium was essential for binding and stimulation of cAMP production. These results indicate that human adrenocortical cells contain a single class of ACTH receptors which are highly similar in affinity, capacity, and calcium requirement to those of rat adrenocortical cells, but differ from the rat receptors in the concentration of ACTH needed for cAMP generation.

Photoreactive, active derivatives of trypsin and chymotrypsin inhibitors from soybeans and chickpeas

The photoreactive arylsufenyl chloride 2-nitro-4-azidophenylsulfenyl chloride (2,4-NAPS-Cl) has been used for the selective modification of tryptophan in Kunitz's soybean trypsin inhibitor (STI). The ultraviolet absorption spectrum and amino acid analysis of 2,4-NAPS-STI indicated that only one of the two tryptophans, 93 or 117, present in STI was modified. Amino acid analysis of the two separated CNBr-cleavage products of 2,4-NAPS-STI showed that only tryptophan 93 underwent modification. 2,4-NAPS-STI fully retained its inhibitory activity against trypsin. The covalent attachment of 2,4-NAPS-STI to tritiated trypsin after photolysis was demonstrated by exclusion chromatography on Sephadex G-50 in the presence of guanidine hydrochloride. Photoreactive derivatives of the Bowman-Birk trypsin-chymotrypsin inhibitor (BBI) from soybeans and of CI, the trypsin-chymotrypsin inhibitor from chick peas were prepared by selective modification of the epsilon-amino groups of 2,4(5)-NAPS-Cl. The ultraviolet absorption spectra of the photolabeled inhibitors indicated that three out of the five lysines of BBI and one of the seven lysines of CI were modified. The inhibitory activity of the modified inhibitors towards trypsin and chymotrypsin was not reduced even after photolysis. The specific lysine residues that constitute the trypsin-inhibitory sites of BBI and CI did not react with the photoreactive reagents. Further modification of the photoreactive derivatives of BBI and CI with maleic anhydride, directed towards the trypsin-reactive sites, resulted in almost complete loss of trypsin-inhibiting activity without reducing the ability to inhibit chymotrypsin. A pronounced potentiation effect (approximately 2x) of the chymotrypsin inhibiting activity was noted for 2,5-NAPS-CI and it was retained even after maleylation followed by photolysis, raising the possibility of exposure of an additional chymotrypsin inhibitory site in CI.

Urea treatment allows dithiothreitol to release the binding subunit of the insulin receptor from the cell membrane: implications for the structural organization of the insulin receptor

The sequence of the human insulin receptor has only one identifiable transmembrane region which is located in the beta subunit. The structure predicts that the alpha subunit, which binds insulin, is attached to the cell only by disulfide bonds to the beta subunit. However, treatment of membranes with dithiothreitol is ineffective at releasing the alpha subunit. If the receptor structure is unfolded with urea, dithiothreitol is able to release the alpha subunit. These data provided confirmatory evidence that the alpha subunit is not a transmembrane protein.

Preparation of photoreactive derivatives of trypsin-chymotrypsin inhibitors from soybeans and chick peas by selective modification of lysine residues

Photoreactive derivatives of the Bowman-Birk trypsin-chymotrypsin inhibitor (BBI) from soybeans and of CI, the trypsin-chymotrypsin inhibitor from chick peas, were prepared by selective modification of the epsilon-amino groups of lysine residues with 2-nitro-4(5)-azidophenylsulfenyl chlorides (2,4(5)-NAPS-C1). The ultraviolet absorption spectra of the photolabeled inhibitors indicated that three out of the five lysines of BBI and one of the seven lysines of CI were modified. The inhibitory activity of the modified inhibitors towards trypsin and chymotrypsin was not reduced even after photolysis. The specific lysine residues that constitute the trypsin-inhibitory sites of BBI and CI did not react with the photoreactive reagents. Further modification of the photoreactive derivatives of BBI and CI with maleic anhydride, directed towards the trypsin-reactive sites, resulted in almost complete loss of the trypsin-inhibiting activity without reducing the ability to inhibit chymotrypsin. A pronounced potentiation effect (approximately 2x) of the chymotrypsin inhibiting activity was noted for 2,5-NAPS-CI and it was retained even after maleylation followed by photolysis, raising the possibility of exposure of an additional chymotrypsin inhibitory site in CI.

A prolactin-inhibiting factor within the precursor for human gonadotropin-releasing hormone

The cloned complementary DNA sequence encoding the human gonadotropin-releasing hormone (GnRH) precursor protein was used to construct an expression vector for the bacterial synthesis of the 56-amino acid GnRH-associated peptide (GAP). GAP was found to be a potent inhibitor of prolactin secretion and to stimulate the release of gonadotropins in rat pituitary cell cultures. Active immunization with peptides corresponding to GAP sequences led to greatly increased prolactin secretion in rabbits.

The role of extracellular calcium in corticotropin-stimulated steroidogenesis

The role of extracellular Ca2+ in the binding of corticotropin (ACTH) to adrenocortical cell receptors as well as in the post-binding events involved in steroidogenesis were investigated. Binding studies using [125I-Tyr23,Phe2,Nle4]ACTH (1-38) peptide showed that extracellular Ca2+ is essential not only for the interaction of ACTH with its receptor, but also for continued occupancy of the receptor. In view of the requirement of Ca2+ for binding the hormone to the receptor, the role of Ca2+ in post-receptor events was investigated by covalently attaching the hormone to its receptor by photoaffinity labeling in the presence of Ca2+. Persistent activation of steroidogenesis induced by photoaffinity labeling in the presence of Ca2+ was depressed when cells were incubated in medium containing EGTA but was unaffected when the cells were merely washed and incubated in Ca2+-free medium. In the presence of EGTA, 8-Br-cAMP partially restored persistent activation of steroidogenesis. The concentration of extracellular Ca2+ required for restoring steroidogenesis was 10-fold lower than the concentration of Ca2+ needed for optimal binding of ACTH to its receptor. These results suggest that the primary role of extracellular Ca2+ in the action of ACTH is to facilitate the association of the hormone with its receptor.

Characterization of adrenocorticotropin receptors that appear when 3T3-L1 cells differentiate into adipocytes

The binding of an 125I-labeled analog of ACTH, [125I]Tyr23,Phe2,Nle4-ACTH-(1-38), to differentiated 3T3-L1 fat cells was characterized. Time-dependent binding, which was inhibited by saturating concentrations of unlabeled ACTH (0.44 microM), could be demonstrated in the differentiated cells. Using 0.4 nM [125I]ACTH analog and increasing concentrations of ACTH, the half-maximal concentration for inhibition by ACTH was 4.3 nM. Scatchard analysis demonstrated a single class of ACTH binding. There were approximately 3500 binding sites/cell. The binding of [125I]ACTH analog was specific in that it could be displaced by ACTH, ACTH-(1-19), ACTH-(1-17), and N-acetyl-Ser1-ACTH, but not by high concentrations of insulin, beta-endorphin, or polylysine. There was an excellent correlation between the ability of ACTH and its analogs to inhibit [125I]ACTH analog binding and the ability of ACTH and its analogs to stimulate cAMP production. In contrast, no saturable binding could be demonstrated when undifferentiated 3T3-L1 fibroblasts, which are not responsive to ACTH, were studied. Thus, differentiation of 3T3-L1 cells into the adipocyte form is accompanied by the appearance of receptors for ACTH. These receptors allow the adipocytes to respond to ACTH.

Topological mapping of acetylcholine receptor: evidence for a model with five transmembrane segments and a cytoplasmic COOH-terminal peptide

Antibodies were raised against two synthetic peptides whose sequences correspond respectively to the COOH-terminal end (residues 501-516) of the protein encoded by the gene for the delta chain and to a proposed cytoplasmic region (residues 350-358) of the beta chain of the acetylcholine receptor from Torpedo californica. Binding of the COOH-terminal antibody to the acetylcholine receptor in intact, receptor-rich vesicles was tested by radioimmunoassay and by precipitation with immobilized protein A. In both cases, binding was detected only after treatment of the vesicles with detergent, suggesting that the segment of the receptor that is recognized by this antibody is on the cytoplasmic side of the membrane. Electron microscopy of tissue from Torpedo electric organ labeled with colloidal gold-conjugated second antibodies established that both anti-receptor antibodies bind to the cytoplasmic surface of the postsynaptic membrane. These experiments give ultrastructural evidence that the COOH-terminal segment of the delta chain as well as residues 350-358 of the beta chain are on the cytoplasmic surface. They strongly support a model in which each of the receptor subunits crosses the membrane five times in which one transmembrane segment of each chain contributes to the formation of a central ion channel.

Preparation and characterization of photoreactive derivatives of GnRH. Persistent activation of function by photoaffinity labeling

A photoreactive derivative of the highly potent gonadotropin releasing hormone (GnRH) agonist, D-Lys6-GnRH(1-9)-ethylamide, was prepared by selective modification of the epsilon-amino group with 2-nitro-4-azidophenyl sulfenyl chloride (2,4-NAPS C1). The modified peptide [D-Lys(NAPS)]6-GnRH-(1-9)-ethylamide was found to be a full agonist of LH release from rat pituitary cells with a relative potency 23 compared to GnRH. Covalent attachment of the photoreactive analog to rat pituitary cells resulted in prolonged activation of LH secretion which could not be inhibited by a potent GnRH antagonist. Persistent stimulation of pituitary gonadotrophs caused by covalently bound hormone led to desensitization of the LH releasing mechanism.

The effects of synthetic locust adipokinetic hormone on dispersed locust fat body cell preparations: cAMP induction, lipid mobilization, and inhibition of protein synthesis

A procedure for the preparation of functional cells from adult locust fat bodies by collagenase treatment has been developed. The high variability of replicates encountered when whole fat bodies are incubated in vitro is greatly reduced in incubation of the dispersed cells. Synthetic locust adipokinetic hormone (AKH) (40 nM) stimulated release of lipids from the dispersed fat body cells at a rate comparable to that observed using whole fat bodies in vitro. Synthetic AKH elevated cAMP levels sixfold in dispersed cells. In addition, AKH inhibited protein synthesis to a maximum of 50-70% in a concentration-dependent manner. None of these actions of AKH required the presence of locust hemolymph components. These results demonstrate the utility of the isolated locust fat body cells for investigating hormonal action in vitro.

Radioimmunocytochemistry using a tritiated goat anti-rabbit second antibody

Affinity-purified goat anti-rabbit immunoglobulin G (GAR) was conjugated with (3H)-propionyl succinimidate and used to localize substance P (SP), enkephalin (ENK), and serotonin immunoreactive sites in the spinal dorsal horn and medulla of the rat and cat. Autoradiographic localization was demonstrated on paraffin, frozen, Vibratome, and 2 micron plastic sections. The latter were obtained from radiolabeled Vibratome sections that were embedded in epoxy resin. The distribution of SP, ENK, and serotonin demonstrated by radioimmunocytochemistry was comparable to that observed on semiadjacent sections using peroxidase-antiperoxidase (PAP) immunocytochemistry. The autoradiograms, however, were generated using primary antibody concentrations up to five times more dilute than concentrations used for the PAP procedure. Indirect radioimmunocytochemistry using a (3H) anti-immunoglobulin G second antibody can be used to localize a variety of monoclonal and polyclonal antisera. It is quantifiable at the light microscopic level and can be potentially used with peroxidase histochemistry to double label immunoreactive structures at the ultrastructural level.

Population growth and distribution versus agricultural change: an analysis of the Warli tribal community in Dahanu and Talaseri Talukas of Thane district (Maharashtra)

The authors examine the relationship between population growth and agricultural change using a village-level study of the Warli tribal community in Maharashtra, India. "This paper tries to highlight the relationship that exists between the two factors and the relative changes in the structural character of the two factors. It also focuses on the complications brought about by the juxtaposition of a market economy of the nontribals on the subsistence peasant agriculture of the Warli tribals. Methodology is empirical. Suitable statistical aids have been used on available census material [for the years 1901-1971], substantiated with fieldwork."

Preparation of a specifically tritiated locust adipokinetic hormone analog with full biological potency

A synthetic peptide related to locus adipokinetic hormone ( AKH ) and shrimp red pigment concentrating hormone ( RPCH ) containing a tyrosine residue in place of phenylalanine was iodinated and the 3,5- diiodotyrosyl derivative was isolated by reverse phase HPLC. Catalytic dehalogenation of the diiodo derivative in the presence of tritium yielded the tritiated AKH analog which was isolated by gel filtration on Sephadex LH-20 and reverse phase HPLC. The tritiated peptide was formed to be identical to AKH in its ability to stimulate lipid release into the hemolymph of locusts in vivo where the diiodotryrosyl derivative was inactive. The specific radioactivity of the tritiated peptide was 57.2 Ci/mmol, or 99% of the theoretical value.

Unusual CT scan findings in pseudohypoparathyroidism

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Mechanisms of adrenocortical depression during Escherichia coli shock

The response of the adrenal cortex to corticotropin during sepsis is variable. We have previously demonstrated a significant decrease of corticosterone production by rat adrenocortical cells in response to corticotropin stimulation after incubation with septic shock plasma (SP) as compared with control plasma (CP). We have studied the mechanisms of this depression. The following defects were demonstrated. (1) Cells bound less radioiodinated corticotropin analog after SP treatment (2.9 +/- 0.4 femtomoles/50 micrograms DNA) than after CP treatment (6.4 +/- 0.3 fmole/50 micrograms DNA). (2) Cyclic adenosine monophosphate (cAMP) production was less after SP treatment (59.3 +/- 4 pmole per 10(5) cells per two hours) compared with CP treatment (110.3 +/- 11.3 pmole per 10(5) cells per two hours). (3) Exogenously added dibutyryl cAMP was unable to correct the defect in corticosterone production after SP treatment (4.96 +/- 0.7 micrograms/24 hr) as compared with CP treatment (6.99 +/- 0.5 micrograms/24 hr). Our studies suggest this defect is located in the synthesis of pregnenolone from cholesterol. These mechanisms may be responsible for the low cortisol levels previously observed in humans during septic shock.

Amino acid sequence of retinal transducin at the site ADP-ribosylated by cholera toxin

Transducin was [32P]ADP-ribosylated by cholera toxin in bovine retinal rod outer segments and then partially purified on omega-amino octyl agarose to remove other ADP-ribosylated proteins. Trypsin digestion of the ADP-ribosylated transducin and further purification using boronate-polyacrylamide beads and high performance liquid chromatography yielded a single radiolabeled tetrapeptide, Ser-Arg-Val-Lys. The ADP-ribose is linked to the guanidinium group of arginine.

A rapid sensitive assay for the quantitation of elastin

A rapid, sensitive and direct assay was developed for the quantitation of elastin using reverse phase high performance liquid chromatography. The method is based on the separation of the alkaline hydrolysis-resistant dipeptide valyl-proline, a dipeptide found in high concentrations in elastin. The methodology is applicable to unlabelled elastin samples in the range of 10-100 micrograms utilizing fluorescamine detection and to hot alkali insoluble as well as soluble forms of elastin. Increased sensitivity was achieved by the use of in vitro radiolabelling of elastin with [3H]proline. This was useful for following synthesis of elastin in cultured cells. Since this technique is not dependent on detection of the elastin-specific crosslink groups, desmosine and isodesmosine, precursor forms of elastin can be measured as well as other forms of elastin deficient in cross-linking. The same chromatographic procedure however, is able to detect these desmosine and isodesmosine crosslinks. Therefore, in cell cultures under the proper radiolabelling conditions, biosynthesis and cross-linking of elastin can be followed simultaneously in a single chromatographic procedure.

Corticotropin receptors, cyclic AMP and steroidogenesis

The detection and characterization of the physiologically relevant receptors for corticotropin (ACTH) in rat adrenocortical cells is described. By the use of a radioligand with full biological potency and high specific radioactivity (1800 +/- 75 Ci/mmol), a single class of receptors with an apparent Kd of 1.41 +/- 0.21 nM was detected and the number of sites was estimated to be 3840 +/- 1045 per cell. The binding curve was superimposable on the concentration-response curve for cAMP but dissociated from that for steroidogenesis. These data are best explained by the receptor-reserve model in which occupancy of a small fraction of the receptors is sufficient for inducing maximal steroidogenesis.

Photoreactive derivative of Kunitz's soybean trypsin inhibitor. Preparation by selective modification of a tryptophan residue and formation of a covalent complex of the modified inhibitor with trypsin

The photoreactive arylsulfenyl chloride 2-nitro-4-azidophenylsulfenyl chloride (2,4-NAPS-Cl) has been used for the selective modification of tryptophan in Kunitz's soybean trypsin inhibitor (SBTI). The ultraviolet absorption spectrum and amino acid analysis of 2,4-NAPS-SBTI indicated that only one of the two tryptophans (93 or 117) present in SBTI was modified. CNBr cleavage of 2,4-NAPS-SBTI resulted in two fragments 1-114 and 115-181. Amino acid analysis of the two separated fragments showed that only tryptophan 93 underwent modification. 2,4-NAPS-SBTI fully retained its inhibitory activity against trypsin. The photoaffinity labeling of trypsin with 2,4-NAPS-Cl was performed on tritiated trypsin prepared by reacting bovine trypsin with [3H]-succinimidyl propionate. The covalent attachment of 2,4-NAPS-SBTI to the tritiated trypsin after photolysis was demonstrated by exclusion chromatography on Sephadex G-50 in the presence of guanidine hydrochloride.

Chemical and biological characterization of salmon melanocyte-stimulating hormones

Ten peptides related to melanocyto-stimulating hormone (MSH) have been identified in an acid acetone extract of the chum salmon pituitary. All these peptides are related to the alpha-MSH and beta-MSH families, but no peptide related to gamma-MSH has been found. This result is in accordance with the finding that the gamma-MSH segment is deleted from the N-terminal peptide of salmon pro-opiocortin (NPP I). Based on the structures of newly isolated peptides, the maturation process of MSH is discussed. The major components of salmon MSH were tested for biological activities. In the lipolytic assay with rabbit fat cells, alpha-MSH I and alpha-MSH II were equipotent, but beta-MSH I and NPP I exhibited very low or no activity. On the other hand, the des-acetyl-alpha-MSH I was found to be four times as potent as alpha-MSH I in this assay. The steroidogenic activities of alpha-MSH I and N-des-acetyl-alpha-MSH I were approximately 0.05% of the potency of ovine ACTH. All other peptides exhibited less than 0.01% potency. Salmon alpha-MSHs were found to be somewhat more potent melanophore-stimulating agents than the beta-MSHs.

Determination of locust vitellogenin by radioimmunoassay with [3H]Propionyl-vitellogenin

A simple procedure for radiolabeling of locust vitellogenin is described. This procedure involves coupling of [3H]propionyl succinimidate to purified vitellogenin with high yield and specific activity. Using this radiolabeled analog, a specific and sensitive radioimmunoassay was developed for determining locust vitellogenin content, with a lower detection limit of 1 ng. [3H]Propionyl-vitellogenin binds completely to rabbit anti-vitellogenin (locust) and can be completely competed out by locust vitellogenin. The structural similarity of locust vitellogenin with that of locust egg vitellin, male locust lipophorin (a diglyceride-carrying lipoprotein), Xenopus laevis vitellogenin, and chicken egg yolk lipovitellin was examined with this RIA procedure. Comparable binding competition was obtained with locust vitellin only. Male locust lipophorin, Xenopus vitellogenin, and chicken lipovitellin did not inhibit vitellogenin binding at concentrations 1000-fold greater than that of locust vitellogenin. The use of this RIA in determination of vitellogenin synthesis in vivo and in vitro, using isolated fat body preparations, is described.

Cardiovascular responses to alpha-melanocyte stimulating hormone during the perinatal period in sheep

To determine the effects of alpha-melanocyte stimulating hormone (alpha MSH) on the circulation of undisturbed fetal sheep and young lambs and to explore possible mechanisms of actions, we examined the responses of ascending aortic blood flow, heart rate, stroke volume, and arterial blood pressure to a single intravenous injection of alpha MSH, ACTH, cortisol and to alpha MSH after beta-adrenergic blockade. We also measured cardiac output and organ blood flows before and after alpha MSH injection by the radionuclide labeled microsphere technique. alpha MSH increased ascending aortic blood flow from 249 +/- 23 to 327 +/- 30 ml X min-1 X kg-1 (P less than 0.001), heart rate from 111 +/- 10 to 126 +/- 11 min-1, (P less than 0.001) and stroke volume from 2.32 +/- 0.21 to 2.75 +/- 0.20 ml X kg-1, (P less than 0.001) in 10 young lambs 15-30-day-old. alpha MSH decreased mean systemic arterial blood pressure from 42.6 +/- 1.7 to 39.3 +/- 1.6 mmHg (P less than 0.001) in fetal sheep and min-1, (P less than 0.001) and stroke volume from 2.32 +/- 0.21 to 2.75 +/- 0.20 ml X kg-1, (P less than 0.001) in 10 young lambs 15-30-days-old. alpha MSH decreased mean systemic arterial blood pressure from 42.6 +/- 1.7 to 39.3 +/- 1.6 mmHg (P less than 0.001) in fetal sheep and from 77.5 +/- 4.5 to 72.7 +/- 4.3 mmHg (P less than 0.001) in young lambs. In six additional young lambs (20-35-day-old) cardiac output, measured by microspheres, increased with alpha MSH from 216 +/- 20 to 261 +/- 19 ml X min-1 X kg-1 (P less than 0.001). alpha MSH also increased blood flow to the myocardium from 104 +/- 22 to 151 +/- 26 ml X min-1 X 100 g-1 (P less than 0.001), to the adrenals from 195 +/- 38 to 243 +/- 41 ml X min-1 X 100 g-1, (P less than 0.05), and to the lungs from 157 +/- 31 to 468 +/- 81 ml X min-1 X 100 g-1 (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of corticotropin receptors on rat adipocytes

Synthetic [125I]-Tyr23, Phe2, Nle4-adrenocorticotropin (ACTH)-(1-38) [( 125I]-ACTH analog) with full biological potency and near theoretical specific radioactivity (1800 +/- 75 Ci/mmol) was used to investigate ACTH receptors on isolated rat adipocytes derived from 42-day-old rats. Binding to adipocytes was studied in the presence of 1% bovine serum albumin (BSA) as well as 4% BSA. The interaction of the [125I]-ACTH analog with adipocytes was highly specific, rapid, saturable, and reversible. Scatchard analysis of the binding data obtained in medium containing 1% BSA revealed a single class of binding sites with an apparent KD = 170 +/- 11.9 pM. Competition experiments with unlabeled ACTH also yielded a comparable value for the apparent KD (143 +/- 16.5 pM). The number of receptors per adipocyte was quite low (521-841/cell). The stimulation of lipolysis by ACTH was closely correlated with the binding, the apparent Km being 145-177 pM. At a concentration of 4% BSA in the incubation medium, the binding curve was shifted significantly to the right (apparent KD = 446 +/- 77 pM) and the binding capacity was also significantly enhanced (1663 +/- 208/cell) without any change in the apparent Km for glycerol release (187 +/- 7.1 pM).

Studies on corticotropin-induced desensitization of normal rat adrenocortical cells

The effects of prior exposure of normal rat adrenocortical cells to ACTH on the responsiveness of the cells to subsequent stimulation with the hormone have been studied. ACTH induces a time- and concentration-dependent refractoriness of both cAMP formation and steroidogenesis. Desensitization of either response was observed only upon activation of the response. Thus, both ACTH and 8-Br-cAMP caused desensitization of the steroidogenic response. The ACTH-induced desensitization of steroidogenesis, however, was completely prevented by blocking the steroidogenic action of ACTH with aminoglutethimide during exposure of cells to the hormone. Aminoglutethimide had no effect on ACTH-induced desensitization of the cAMP response. Studies with analogs of the hormone also confirmed that induction of desensitization of the steroidogenic response is independent of the desensitization of the cAMP response. Binding studies showed that the insignificant decrease in ACTH receptors could not account for the large changes in the responsiveness induced by prior exposure of cells to ACTH. Desensitization of the steroidogenic response appears to result from a defect in the rate-limiting first step of the steroidogenic pathway, namely conversion of cholesterol to pregnenolone.

Mechanism of induction of delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity in rat adrenocortical cells by corticotropin

The regulation of delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD) was studied in primary cultures of rat adrenocortical cells. In the absence of ACTH, this enzymic activity was found to decay with a half-life of 3.1 days, which was similar to the half-life of the enzyme activity induced by ACTH in vitro (3.5 days). The increase in 3 beta-HSD activity was highly specific for ACTH and dibutyryl cAMP; the activity was not increased by other hormones known to affect adrenocortical growth or function. The induction of 3 beta-HSD activity by ACTH or dibutyryl cAMP required a lag period of approximately 4 h and was dependent on RNA and protein syntheses. The increase in 3 beta-HSD activity observed after ACTH treatment was not a result of ACTH-induced inhibition of degradation of the enzyme, nor was it due to the synthesis of a soluble intermediate which could directly activate the enzyme. ACTH stimulated the incorporation of [35S]methionine into a protein associated with 3 beta-HSD activity detected on polyacrylamide gels after electrophoresis of Triton X-100 extracts of adrenocortical cells. The induction of this protein by ACTH was inhibited by actinomycin D. A protein band of a partially purified preparation of rat adrenal 3 beta-HSD was found to comigrate with the ACTH-induced protein on sodium dodecyl sulfate-polyacrylamide gel. These results suggest that ACTH caused the de novo synthesis of 3 beta-HSD by a mechanism dependent on RNA synthesis.

Synthesis of human corticotropinyl-thiolglycine and its specific conjugation to bovine serum albumin

Human corticotropin containing a thiolglycine residue at the carboxyl terminal (I) was synthesized by the solid-phase method. The citraconyl derivative of peptide I was coupled to either a model tetrapeptide or bovine serum albumin by reaction with silver nitrate/N-hydroxysuccinimide in water. The extent of reaction with bovine serum albumin was determined by radioimmunoassay, and the peptide-protein conjugate was shown to possess 12% of the steroidogenic activity of porcine adrenocorticotropin in isolated rat adrenal cells. Peptide I and its conjugate with the model tetrapeptide were fully active in the same system.

Photoaffinity labeling of the canine renal receptor for parathyroid hormone

Studies were undertaken to identify and characterize components of the parathyroid hormone receptor. An analog of the bovine parathyroid hormone(1-34) sequence was derivatized at the 23-tryptophan position with the photoreactive reagent 2-nitro-5-azidophenylsulfenyl chloride. 2-Nitro-5-azidophenylsulfenyl-bovine parathyroid hormone (NAPS-bPTH) analog retained full biological activity with respect to receptor binding and activation of adenylate cyclase in canine renal cortical plasma membranes. 125I-bPTH(1-34) analog was also derivatized without loss of receptor-binding activity. When 125I-NAPS-bPTH(1-34) analog was incubated with canine renal plasma membranes and then photolyzed, at least two 125I-labeled membrane components were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The incorporation of 125I radioactivity into one of these components (Mr congruent to 60,000) was inhibited when incubation and photolysis were performed in the presence of excess, unlabeled bPTH(1-34). Furthermore, photolysis of membranes in the presence of NAPS-bPTH(1-34) analog led to activation of adenylate cyclase which persisted following washing to remove noncovalently bound peptide, suggesting a functional, covalent hormone-receptor complex had been formed. We conclude that the M r congruent to 60,000 membrane component may be a part of the renal receptor for parathyroid hormone.

Characterization of corticotropin receptors on adrenocortical cells

The binding of corticotropin (ACTH) to receptors on isolated rat adrenocortical cells was investigated with the aid of [[125I]ITyr23, Phe2, Nle4]ACTH-(1-38) (125I-ACTH analog) which retained full biological potency and had a specific radioactivity of 1800 +/- 75 Ci/mmol. Binding was highly specific to adrenocortical cells, and the radioactive peptide was displaced by low concentrations of ACTH but not by other basic peptides. Binding was rapid, reversible, and linearly related to the number of cells. 125I-ACTH analog was not significantly degraded by incubation with the cells at 23 degrees C for 1 hr. Scatchard analysis of the binding was compatible with a single class of binding sites with Kd = 1.41 +/- 0.21 nM, and the number of sites was estimated to be 3840 +/- 1045 per cell. The binding curve was superimposable on the concentration-response curve for cyclic AMP. Small, but significant amounts of 125I-ACTH analog were bound at concentrations sufficient for maximal stimulation of steroidogenesis. For a series of ACTH analogs, the concentrations of the peptides required for half-maximal stimulation of cyclic AMP production were in excellent agreement with the concentration required for half-maximal inhibition of binding. These results suggest that the adrenocortical cells contain only one class of ACTH receptors and that stimulation of a small fraction of these receptors (less than 3%) is sufficient for maximal steroidogenesis.

Persistent activation of steroidogenesis in adrenocortical cells by photoaffinity labeling of corticotropin receptors

Photolysis of rat adrenocortical cells in the presence of the photoreactive derivative [(2-nitro-5-azidophenylsulfenyl)Trp9]-adrenocorticotropic hormone (2,5-NAPS-ACTH) at 24 degrees C resulted in persistent activation of corticosterone production. The basal rate of steroidogenesis became maximal when photolysis was performed at 24 degrees C but remained the same as that of control cells when irradiation was performed at 0 degrees C. No increase in basal rate was observed with dark controls or cells photolyzed with [(2,4-dinitrophenylsulfenyl)Trp9]ACTH, a photoresistant analog of the hormone. Prephotolyzed 2,5-NAPS-ACTH failed to induce persistent activation. Both ACTH and 2,4-(dinitrophenylsulfenyl)Trp9-ACTH blocked the photo-induced activation of steroidogenesis elicited by 2,5-NAPS-ACTH. Under photolysis conditions which caused the basal rate of steroidogenesis to become maximal, a 3-fold increase in the basal rate of cAMP formation was observed.

Comparison of the structural features of corticotropin required for stimulation of steroidogenesis and cAMP production in rat and rabbit adrenocortical cells

The steroidogenic activities of ACTH, alpha-MSH, beta-MSH as well as analogs of the hormones have been compared in rat and rabbit adrenocortical cells. ACTH is equally active in both species and the melanotropins have very low steroidogenic potency in either species. The steroidogenic potencies of the peptide analogs are strikingly similar in the two species, suggesting that the structural requirements for eliciting steroidogenesis are the same in rat and rabbit adrenocortical cells. The analog NPS-ACTH has low, comparable steroidogenic activity in both species. NPS-ACTH is a potent antagonist of ACTH-induced cAMP production in rat adrenocortical cells but acts as a weak partial agonist in rabbit adrenocortical cells. These results suggest that steroidogenesis may be mediated by receptors different from those involved in the cAMP response observed at supraphysiological concentrations of ACTH.

Synthesis of a corticotropin analog that retains full biological activity after iodination

In order to circumvent the drastic decrease in biological activity that accompanies iodination of corticotropin, we have synthesized an analog of the human hormone containing phenylalanine in place of tyrosine in position 2 and norleucine in place of methionine in position 4 to give [Phe2,Nle4]ACTH-(1-38). This analog, referred to as Phe2,Nle4-ACTH-(1-38), was purified by ion exchange chromatography and partition chromatography. Phe2,Nle4-ACTH-(1-38) was found to be indistinguishable from synthetic human ACTH in its ability to stimulate corticosterone production in isolated rat adrenocortical cells. Iodination of Phe2,Nle4-ACTH-(1-38) resulted in the formation of monoiodo-Tyr23,Phe2,Nle4-ACTH-(1-38) and diiodo-Tyr23,Phe2,Nle4-ACTH-(1-38), which were completely separated from each other and unmodified Phe2,Nle4-ACTH-(1-38) by reverse phase high performance liquid chromatography. Monoiodo-Tyr23,Phe4,Nle4-ACTH-(1-38) was also found to be as potent as ACTH in stimulating steroidogenesis. These results show that Phe2,Nle4-ACTH-(1-38) can be used for the preparation of the radioligand with full biological activity for studying physiologically relevant corticotropin receptors and for use in RIA.

Primary culture of normal rat adrenocortical cells. I. Culture conditions for optimal growth and function

Rat adrenocortical cells retained their differentiated characteristics over 2 wk in culture without a specific requirement for additives other than inorganic salts, amino acids, vitamins, and fetal bovine serum. The cells were maintained free from fibroblast overgrowth by substitution of D-value in place of L-valine in the medium. Corticotropin (ACTH) inhibited the growth of adrenocortical cells in this medium and the effect was reversible. The adrenocortical cells had a limited capacity for growth as reflected by total cell counts and [3H]thymidine uptake with cells from young animals demonstrated a greater potential for DNA synthesis than cells obtained from mature animals. A very sensitive assay for ACTH using a small number of cells in primary culture also is described.

Primary culture of normal rat adrenocortical cells. II. Quantitation of steroid dehydrogenase stain

A simple, rapid procedure for the quantitation of the histochemical stain for delta 5-3beta-hydroxysteroid dehydrogenase (3beta-HSD) in cultured cells is described. Adrenocortical cells were stained for 3beta-HSD and then solubilized with 0.5 N NaOH. The absorbance of the solubilized cell solution was measured at 570 nm and a linear relationship was obtained between the number of cells and the intensity of the absorption. It is shown that the regulation of 3beta-HSD activity in primary cultures of normal rat adrenocortical cells can be monitored by the quantitative histochemical assay. The results show a good correlation with the data obtained by a biochemical assay for the enzyme.

A sensitive radioimmunoassay for corticotropin using a fully biologically active 125I-labeled ligand

The human corticotropin (ACTH) analog, Phe2,Nle4-ACTH-(1-38) was iodinated by the chloramine-T procedure and the product was purified by reverse phase high performance liquid chromatography. The specific radioactivity of [125I]Tyr23,Phe2,Nle4-ACTH-(1-38) was determined by comparing the antiserum binding curves of the iodinated peptide and [3H]ACTH of known specific activity. This method gave a value of 1800 +/- 75 Ci/mmol, which is close to the theoretical radioactivity expected for the introduction of a single 125I atom into the peptide. [125I]Tyr23,Phe2,Nle4-ACTH-(1-38) was as potent as ACTH in stimulating corticosterone production in isolated rat adrenocortical cells. The concentrations for half-maximal steroidogenesis were 36.5 +/- 6.1 pM for the 125I derivative and 37.6 +/- 6.7 pM for ACTH. By the use of this 125I-labeled ligand, a highly sensitive RIA capable of detecting 1 pg aCTH was developed.l The antiserum employed in this study appeared to be directed against residues 11-13 of ACTH.

Preparation of photoreactive derivatives of glutathione and [9-(2-mercaptotryptophan)]corticotropin by selective modification of the sulfhydryl group

The photoreactive arylsulfenyl chlorides 2-nitro-4-azidophenylsulfenyl chloride (2,4-NAPS-Cl) and 2-nitro-5-azidophenylsulfenyl chloride (2,5-NAPS-Cl) have been used for the selective modification of thiol groups in glutathione and [Trp(SH)9]corticotropin (ACTH). Both reagents reacted rapidly with both types of thiol groups to form unsymmetrical disulfides. The photoreactive derivatives of glutathione and [Trp(SH)9]ACTH were stable to neutral and acidic conditions but were readily cleaved above pH 9 and by beta-mercaptoethanol. Photolysis of the NAPS derivatives of [Trp(SH)9]-ACTH at neutral pH resulted in the formation of covalently liked polymers and dimers which yielded monomer upon treatment with beta-mercaptoethanol. Analysis of the amino acid composition of acid hydrolysates of photolysed monomeric and dimeric products indicated a decrease in proline, valine, tyrosine, and phenylalanine.

Identification of the corticotropin binding domain of bovine serum albumin by photoaffinity labeling

The interaction of the pituitary hormone corticotropin (ACTH) with bovine serum albumin (BSA) was investigated by photoaffinity labeling with 2-nitro-4-azido-phenylsulfenyl (2,4-NAPS) derivatives of aCTH and [Trp-(SH)9]ACTH. Nearly 30 mol % of tritiated [2,4-NAPS-Trp9]ACTH was covalently bound to BSA at a molar ratio of hormone:BSA of 1.33. The [2,4-NAPS-Trp9] [3H]ACTH-BSA complex was isolated, and the CNBr fragments of the complex were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The radioactivity was predominantly associated with the amino-terminal CNBr fragment corresponding to residues 1-183 in BSA. This result was confirmed by studies of the inhibition of covalent labeling of BSA by photoreactive ACTH. 8-Anilinonaphthalenesulfonic acid which binds to the amino-terminal domain of BSA strongly inhibited the photolabeling of BSA by [2,4-NAPS-Trp9][3H]ACTH. Palmitate and progesterone, known to bind to the carboxy-terminal domains of BSA, did not inhibit the incorporation of [2,4]NAPS-Trp9][3H]ACTH into BSA. The removal of ACTH from the covalent complexes was also investigated. The release of ACTH from the [2,4]NAPSS-Trp9]ACTH--BSA complex by treatment with beta-mercaptoethanol was complete in 6 h, but only 80% of ACTH was released from [2,4]NAPS-Trp9]ACTH--BSA under these conditions.