Frequencies of Band 3 variants of human red cell membranes in some different populations

A variant of Band 3, the major protein of the erythrocyte membrane, was observed by Mueller and Morrison in 1977 in 6-7% of healthy blood donors on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of erythrocyte membranes treated with pronase. Pronase treated red cells containing this first recognized variant [here designated 'Band 3-Memphis (m)'] section had two bands of about 63,000 and 60,000 Mr while pronase treated normal cells had only the lighter Mr band. The present study includes data on the frequency of variants resembling Band 3-Memphis in patients of different ethnic groups and on random donors obtained earlier in Memphis. These variants were detected by the original method of Mueller and Morrison and were not associated with recognized clinical or haematological abnormalities. Significantly higher gene frequencies for the variants of the (m) type were observed in American Indians, African Americans and Filipinos than in Caucasians; putative heterozygotes and homozygotes were identified among each of these groups. The frequency of silent Band 3 polymorphisms in different populations should be considered in the interpretation of clinical findings associated with the presence of Band 3 variants.

The INR--a help or a hindrance to warfarin dosage?

We have examined the INR values of 128 warfarin patients obtained by four different techniques in common use in Scotland namely venous and capillary. Thrombotest and venous and capillary Prothrombin Time (PT). The PT INRs were carried out using Manchester Reagent thromboplastin. Discrepant INR values were obtained. The mean Manchester venous INR values were lower than those obtained by the other three methods (p less than 0.0001). This suggests that patient's dosed by reference to Manchester venous INR are liable to receive more warfarin than those dosed by the other methods.

Discrepant INR values: a comparison between Manchester and Thrombotest reagents using capillary and venous samples

The International Sensitivity Index (ISI) for different thromboplastin reagents is obtained by calibration against WHO reference preparations. It is hoped that calculation of the International Normalized Ratio (INR) from the ISI will permit accuracy and conformity in reporting laboratory assays of warfarin effect even across a range of different techniques. We have examined the INR values of 128 warfarin patients obtained by four different techniques in common use, namely venous and capillary Thrombotest and venous and capillary Manchester reagent. Discrepant INR values were obtained. The mean Manchester venous INR values were lower than those obtained by the other three methods (P less than 0.0001). This suggests that patients dosed by reference to Manchester venous INR are liable to receive more warfarin than those dosed by the other methods.

New etiology for intestinal uptake of thallium-201

A patient with both rest and exercise thallium images for unstable angina demonstrated marked large intestinal uptake of thallium. However, the thallium uptake in the large intestine was noted only after exercise. The only change in the patient status between the two studies was the administration of verapamil. Thus, verapamil administration has been demonstrated to be a new cause for gut uptake of thallium.

Cognitive-behavioral treatment of recurrent nonspecific abdominal pain in children: an analysis of generalization, maintenance, and side effects

From 10% to 15% of school-aged children experience recurring abdominal pain. This study evaluated the efficacy of a cognitive-behavioral program for the treatment of nonspecific recurrent abdominal pain (RAP) using a controlled group design. The multicomponent treatment program consisted of differential reinforcement of well behavior, cognitive coping skills training, and various generalization enhancement procedures. Multiple measures of pain intensity and pain behavior were conducted, including children's self-monitoring, parent observation, teacher observation, and observation by independent observers. Results showed that both the experimental and the control groups reduced their levels of pain. However, the treated group improved more quickly, the effects generalized to the school setting, and a larger proportion of subjects were completely pain-free by 3-months follow-up (87.5% vs. 37.5%). There was no evidence for any negative side effects of treatment.

Ca2+-mediated catabolism of human erythrocyte band 3 protein

Catabolism of human erythrocyte membrane band 3 protein in the presence of Ca2+ was studied. An increase in the amount of a 30 kDa amino terminal fragment of band 3 was observed when erythrocyte membranes were incubated for 30 min with 1 mM Ca2+ in the presence of whole erythrosol. Incubation of the membranes with Ca2+ alone did not result in band 3 breakdown. Generation of the 30 kDa fragment from band 3 was related to the action of a leupeptin-sensitive Ca2+-dependent proteinase in the cytosol. This proteinase was also responsible for the increased production of a 52 kDa and a 70 kDa transmembrane carboxyl terminal fragment of band 3. From the size of the generated fragments, it is deduced that in the presence of Ca2+ and Ca2+-dependent proteinase, band 3 protein is cleaved at the cytoplasm/membrane interface and along its cytoplasmic domain.

Plasma GABA, GABA-like activity and the brain GABA-benzodiazepine receptor complex in rats with chronic hepatic encephalopathy

Plasma gamma-aminobutyric acid (GABA)-like activity, plasma GABA and the brain GABA-benzodiazepine receptor complex were studied in rats with chronic hepatic encephalopathy. Portal vein ligation (after prior subcutaneous transposition of the spleen) results in complete portal bypass of splanchnic blood. In addition, significant hepatocellular damage was superimposed on this model of portosystemic shunting by ligation of the common bile duct. Plasma GABA-like activity (determined by radioreceptor assay) and true plasma GABA concentrations (determined by high-performance liquid chromatography) were found to be significantly increased in both portal vein-ligated and portal vein and bile duct-ligated rats, compared with controls. However, plasma GABA-like activity was consistently greater than the concentration of true GABA in the plasma of all rats. This suggested the presence of a GABA-like factor in plasma that can inhibit [3H]GABA binding, but is not GABA itself. The concentration of this GABA-like factor was significantly increased in the plasma of rats with chronic hepatic encephalopathy. Despite the significant increase in plasma GABA-like activity and plasma GABA concentrations, there was no alteration in the affinity or density of the physiologically relevant, low-affinity brain GABA binding site in the rats with portal vein ligation, with or without bile duct ligation. There was also no significant alteration in brain benzodiazepine binding in these rats. GABA enhancement of benzodiazepine binding was unchanged in the portal vein-ligated rats. However, the maximal enhancement of benzodiazepine binding was decreased in the rats with portal vein and bile duct ligation. There appears to be no substantial evidence that brain GABAergic neurotransmission is increased in these models of chronic hepatic encephalopathy.

Red blood cell homeostasis: recognition of distinct types of damaged homologous red blood cells by a mouse macrophage cell line

The mouse macrophage (M phi) cell line IC-21 preferentially ingests a subpopulation of homologous red blood cells (MRBC) from normal mice. This subpopulation presumably bears the so-called transfusion lesion, a consequence of damage acquired during the drawing and processing of blood. To determine if all damaged MRBC were recognized by a common receptor site on IC-21 M phi, we prepared suspensions of MRBC damaged in vitro by treatment with tannic acid and compared the phagocytic uptake of these cells with those bearing the transfusion lesion. Trypsin treatment of IC-21 M phi rendered them unable to recognize MRBC bearing the transfusion lesion; but it had no effect on the uptake of tannic acid-damaged MRBC, showing that IC-21 M phi have separate recognition sites for these two populations of damaged MRBC.

Membrane skeletal alterations during in vivo mouse red cell aging. Increase in the band 4.1a:4.1b ratio

We have examined membrane protein profiles for alterations during red blood cell aging. To obtain populations of in vivo-aged red cells, we maintained mice in a state of continuous erythropoietic suppression for up to 8 wk using serial hypertransfusion. The circulating t1/2 of red cells from mice which had been erythropoietically suppressed for 8 wk was less than 1 d compared with a t1/2 of 15 d for red cells from normal animals. The most obvious alteration in membrane proteins was an increase in the ratio of the membrane skeletal components 4.1a:4.1b from 0.3 for the normal red cell population to greater than 1 for these old cells. The 4.1a:4.1b ratio thus appears to be a useful index of red cell age. Analyses of the density profile of cells aged in the hypertransfused mice disclosed that these old cells had a density range similar to that of controls, suggesting that cell density does not increase significantly with red cell age in the mouse.

Phase II evaluation of megestrol acetate in previously treated patients with advanced breast cancer: relationship of response to previous treatment

Thirty-seven patients with advanced breast cancer were treated with megestrol acetate 160 mg daily. All patients except two had been heavily pre-treated with hormonal therapy; eight patients also received chemotherapy. Complete and partial responses occurred in 25% with a mean duration of 5 months (range 2-24 months). A further 38% of patients had static disease for 2 months or greater. Seven patients had previously received medroxyprogesterone acetate, and responses were seen even in patients who had failed to respond to this therapy. This was thought to be due to the higher levels of progestogenic activity which can be routinely achieved with megestrol acetate. Toxicity was minimal, and we would therefore consider that megestrol acetate should be the progestogen of choice in advanced breast cancer.

Erythrocyte homeostasis: antibody-mediated recognition of the senescent state by macrophages

We tested the hypothesis that the accumulation of bound autologous antibody on a "senescent epitope" identifies aged erythrocytes for phagocytic removal by macrophages. Erythrocytes were collected from mice maintained on a hypertransfusion protocol designed to yield cells of defined age. The mouse erythrocytes were assayed for the presence of bound antibody by measuring their susceptibility to ingestion by macrophages from mouse peritoneal exudates and by flow cytofluorometry. Both assays disclosed that only the oldest mouse erythrocytes bore detectable levels of antibody. Flow cytofluorometric analysis revealed that the frequency distribution of IgG isotypes bound to the cells reflected their levels in normal serum. Finally, treatment with trypsin abolished the ability of the macrophages to ingest erythrocytes aged in vivo. These findings support the hypothesis that antibody mediates the clearance of senescent mouse erythrocytes from the circulation and demonstrate that the presence of a trypsin-sensitive recognition structure on macrophages is an essential requirement in this homeostatic process.

Paroxysmal nocturnal hemoglobinuria erythrocytes are of two distinct types: positive or negative for acetylcholinesterase

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired disorder. Erythrocytes isolated from PNH patients show increased sensitivity to complement and decreased acetylcholinesterase (AChE) activity. In this study, indirect immunofluorescence analysis of a monoclonal antibody specific for a surface epitope of human erythrocyte AChE is used to quantitate the content of this enzyme at the single-cell level. Flow-cytofluorimetric analysis of erythrocytes from normal donors indicates that all erythrocytes contain detectable levels of the surface epitope with a strong correlation between cell size and enzyme content. In contrast, erythrocytes from PNH patients show two distinct populations of erythrocytes; namely, those containing a normal content of AChE and a second population containing no detectable AChE. The AChE-negative population of cells is quantitatively complement-sensitive. These data support suggestions that PNH is a clonal disorder resulting in two distinct types of circulating erythrocytes. The abnormal clone produces cells that are both surface-AChE-negative and complement-sensitive. In addition, the method described provides an attractive alternative for the diagnosis and quantitative evaluation of abnormal erythrocytes in PNH patients.

Catabolism of the anion transport protein in human erythrocytes

We identified the catabolic products of protein 3 in human erythrocytes. Protein 3, the major protein of the erythrocyte membrane, functions in anion transport and reacts covalently with tritiated 4,4'-diisothiocyano-1,2-diphenylethane-2,2'-disulfonic acid ([3H]DIDS), a very selective inhibitor of anion transport. In this study, [3H]DIDS was used to label protein 3 in the membranes of normal cells and those from a donor heterozygous for a variant of protein 3, defined by its elongated amino-terminal end. Both types of cells contained [3H]DIDS-labeled peptides other than protein 3. A protein fragment of 60K molecular weight was found in normal cells, whereas both 60K and 63K fragments were identified in cells from the heterozygote. These peptides are identical with those generated by treatment of intact erythrocytes with Pronase or chymotrypsin. A polyclonal rabbit antibody specific for the purified 60K fragment of protein 3 was used to detect this protein and its products in the erythrocyte membrane. Autoradiographs of membrane peptides that were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and allowed to react with the monospecific antibody showed, in addition to protein 3, a 60K fragment and fragments in the 40K region and in the 20-30K region. Cells containing the protein 3 variant yielded two fragments showing a 3K difference in molecular weight in all three regions, demonstrating that degradation of protein 3 is identical in normal erythrocytes and those heterozygous for the variant. This observation also confirms the common derivation of the fragments from protein 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Penicillamine in ankylosing spondylitis: a double blind placebo controlled trial

A double blind placebo controlled trial was carried out over a 6-month period on 17 patients with ankylosing spondylitis (AS) to assess the effect of the second line antirheumatic drug, D-penicillamine. The patients included 13 with peripheral joint involvement. No significant improvement over placebo was detected in a variety of clinical and laboratory indices in the patients receiving active treatment. This controlled trial would not support a use for penicillamine in AS.

A new variant of the anion transport protein in human erythrocytes

The major plasma membrane protein of human erythrocytes is the anion transport protein, termed protein 3. We previously reported a variant form of protein 3 that is elongated on the amino-terminal end of the molecule, which is exposed on the cytoplasmic side of the membrane, but otherwise its features are identical with those of the normal molecule. We have termed this molecule protein 3 variant 1. We now report a new variant form, protein 3 variant 2. The erythrocyte donor was a double heterozygote whose red cells possess a normal protein 3 and a protein 3 variant which is elongated and possesses a second variation at the 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) reactive site. Variant 2 reacts with 4,4'-diisothiocyano-1,2-diphenylethane-2,2'-disulfonic acid (H2DIDS) more readily than does the normal molecule. At high pH values, H2DIDS acts as a bifunctional cross-linking agent; it cross-links the proteolytic products generated by Pronase (or chymotrypsin) treatment of variant 2 less efficiently than noted for normal protein 3 or the first variant. Thus, the newly identified molecule has an alteration at the DIDS reactive site, which is near the outer surface of the membrane. The results can be interpreted as indicating that the DIDS binding site of variant 2 is more exposed than the normal molecule, but further removed from the site on the carboxyl-terminal fragment involved in cross-linking. Although there is a difference in the reactivity of the two protein 3 chains in variant 2, the reaction of variants 1 and 2 and normal cells with varying concentrations of [3H]H2DIDS results in the same amount of incorporation in all cells. Since protein 3 exists as a dimer or higher aggregate in the membrane, these results may indicate an interaction between monomers.(ABSTRACT TRUNCATED AT 250 WORDS)

Phase II study of vincristine, mitomycin-C and mitoxantrone in advanced breast cancer: a preliminary report of response and toxicity

Nineteen patients with advanced, previously treated breast cancer received treatment with vincristine 2 mg i.v., mitomycin-C 6 mg/m2 and mitoxantrone (Novantrone; dihydroxyanthracenedione) 12 mg/m2 i.v. every three weeks. Thirteen patients are evaluable for response and toxicity. Partial remission was seen in six patients, with soft tissue, bone and visceral metastases and static disease in a further four patients. Median duration of response has not yet been reached (8+ months). Toxicity was mild and predictable, with no patient experiencing severe nausea and vomiting, and only four of the patients requiring a wig for alopecia. Malaise and lethargy were common in those patients receiving more than three courses, and an increase in the mean corpuscular volume (MCV) together with a fall in haemoglobin were seen in patients receiving multiple courses of treatment. The study suggests that this combination is active, and may prove useful with other agents in the treatment of breast cancer.

Preferential phagocytosis of in vivo aged murine red blood cells by a macrophage-like cell line

The ability of an established line of mouse macrophages (IC-21) to ingest red blood cells (RBC) aged in vivo was assessed. RBC populations of increasing age were prepared in mice by serial hypertransfusion, a procedure that inhibits erythropoiesis. Mouse RBC with a mean age of about 58 d (normal RBC life span, 60 d) had a circulating half-life of less than 1 d when transfused into normal mice. IC-21 macrophages ingested the in vivo aged RBC in preference to RBC from normal mice (mean RBC age, 30 d). RBC isolated from mice 10 d after being released from one red blood cell lifespan (60 d) of inhibited erythropoiesis (mean RBC age 5 d) were ingested significantly less than RBC from normal mice. The IC-21 macrophage line used with in vivo aged RBC affords a highly defined model system for identifying the mechanism(s) of macrophage-mediated homeostasis.

Reactions of ferryl lactoperoxidase (compound II) with sulfide and sulfhydryl compounds

Lactoperoxidase in the ferryl state (compound II) reacts with sulfide to form a typical sulfheme -containing hemoprotein as do hemoglobin, myoglobin, and catalase. Ferrous sulflactoperoxidase is primarily formed and then oxidized to its ferric form under aerobic conditions. Similar reactions of lactoperoxidase occurs when methylmercaptoimidazole (MMI) is substituted for sulfide. The yield of the adducts from one-turnover reactions of ferryl lactoperoxidase is 100% with sulfide and about 20% with MMI. Sulfur and MMI of the adducts appear to be removed from the enzyme upon reduction by dithionite. Upon the reactions with cysteine and dithiothreitol, the enzyme is converted to spectral species, which are less characteristic but are similar to ferrous and ferric sulflactoperoxidases , respectively. We conclude that there is no essential difference in the mechanism of reactions of lactoperoxidase with sulfide, MMI, cysteine, and dithiothreitol.

Diagnosis and management of hypertension: the stated practices of family physicians

Hypertension is an important and common problem in family practice, but there is no general agreement on the systolic and diastolic pressures at which it should be diagnosed and treated. Responses from 273 family physicians surveyed by mail in Metropolitan Toronto showed a wide variation in the pressures used as cut-off points. The probability that in a given patient hypertension would be diagnosed or treated at different systolic and diastolic pressures varied considerably among the physicians, the variation increasing with the age of the patient. There was also wide variation in opinion among the surveyed physicians about how often patients should be screened for hypertension; depending on the patient's age, up to 35% of the physicians stated that the blood pressure should be measured at every visit. Only one third reported using any one or more methods to ensure that patients with hypertension were not lost to follow-up. The family physicians with an academic appointment used higher cut-off points for diagnosis and treatment, and they screened and scheduled follow-up visits less frequently than those without an academic appointment.

The interaction of human erythrocyte Band 3 with cytoskeletal components

Band 3 of the human erythrocyte is involved in anion transport and binding of the cytoskeleton to the membrane bilayer. Human erythrocytes were treated to incorporate varying concentrations of DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) a non-penetrating, irreversible inhibitor of anion transport, and both functions of Band 3 were analyzed. The rate of efflux of 35SO2-4 was measured and the binding of cytoskeletal components to the membrane was evaluated by extracting the membranes with 0.1 N NaOH and analyzing for the peptides remaining with the membrane. It was found that 0.1 N NaOH extracts all the extrinsic proteins from membranes of untreated cells, while, in the case of the membranes from cells treated with DIDS, a portion of the cytoskeletal components, spectrin (Bands 1 and 2) and Band 2.1 (ankyrin, syndein) remain with the membrane. The amount of these cytoskeletal components remaining with the membrane depends on the concentrations of DIDS incorporated. The effect of DIDS on the extractability of the spectrin-Band 2.1 complex correlates well with DIDS inhibition of anion transport (r = 0.91). At DIDS concentrations which completely inhibit anion transport, about 10% of total spectrin-Band 2.1 complex remains unextracted. Another anion-transport inhibitor, pyridoxal phosphate, has no effect on binding of the cytoskeleton to the membrane. On the other hand, digestion of DIDS-pretreated intact erythrocytes with Pronase, chymotrypsin, or trypsin releases the tight binding of Band 3 to cytoskeleton on the inside of the membrane. Since trypsin does not hydrolyze Band 3 the data suggest that a second membrane protein which is trypsin sensitive may be involved with Band 3 in cytoskeletal binding.

Interaction of a mouse macrophage cell line with homologous erythrocytes

The interaction of the IC-21 murine macrophage cell line and homologous red blood cells (RBC) was assessed in the absence of exogenous opsonins. These results were used to evaluate this system as a potential model for macrophage-mediated clearance of old or damaged RBC. The binding and ingestion of density-separated and unseparated RBC by IC-21 cells were quantitated in assays that involved both 51Cr-labeled RBC and direct microscopy. The number of unseparated RBC that bound to IC-21 macrophages depended on the number of RBC added. Macrophages phagocytized an appreciable proportion of RBC within 3 hours with the ratio of RBC:macrophage of 10, a point at which the RBC-binding was not rate limiting. The mouse RBC were separated into dense- and less-dense fractions which are presumably enriched for old and young cells, respectively. When these RBC fractions were incubated with the IC-21 macrophage, significantly more of these dense cells were phagocytized. These results show that IC-21 macrophage cell line is a useful model for defining the processes whereby aged or damaged RBC are recognized and removed from circulation by macrophages.

Naloxone suppresses food/water consumption in the deprived cat

Intraperitoneal administration of the opiate antagonist, naloxone hydrochloride, resulted in decreased food and water consumption in drug-naive cats. In a cross-over Latin Square design, food consumed by six cats in a one hour period following 23 hours of deprivation, was decreased significantly below control (p less than 0.05) in linear relation to increasing dose (1 mg/kg and 10 mg/kg) of naloxone. Non-linear and time/order effects were not significant. Water consumption was decreased below control in a linear relation to increasing dose (1 and 10 mg/kg) for 5 of 6 cats at the 0.05 significance level. Non-linear and time/order effects on water consumption were not statistically significant for the same 5 cats. These results, and behavioral signs (i.e., vomiting, persistant vocalization, heavy salivation, mydriasis, moderate catatonia, and hissing) occasionally exhibited by four of the six cats in a 1-hr period following injection of the high dose, suggest a malaise-effect of naloxone.

Effect of adenosine on concanavalin A agglutination of human erythrocytes

We have attempted to correlate the functional activity of protein 3 with its activity as a receptor for concanavalin A. The concanavalin A agglutination of human erythrocytes is enhanced by adenosine. It varies with time of storage of the blood and is dependent on the concentration of adenosine in the medium. Adenine and/or inosine, which increase cellular ATP, do not substitute for adenosine in enhancing agglutination, and adenosine enhances agglutination of fresh erythrocytes with normal levels of ATP. Thus, it appears that cellular ATP levels are not directly involved in modulation of concanavalin A agglutination by adenosine. Trypsin, which hydrolyzes most of the exposed proteins of the cell surface but does not alter protein 3, enhances concanavalin A agglutination without altering the relative response to the cell to adenosine. Glucose, as well as the glucose transport inhibitors maltose and cellobiose, inhibits agglutination. High concentrations of adenosine reverse the inhibition by glucose and enhance agglutination in the presence of maltose and cellobiose. Treatment of erythrocytes with 4,4'-diisothiocyanostilbene-2,2-disulfonic acid disodium salt, which selectively inhibits the anion transport function of protein 3, substantially inhibits adenosine-supported concanavalin A agglutination. Treatment of erythrocytes with iodoacetate under conditions in which it selectively reacts with glyceraldehyde-3-phosphate dehydrogenase inhibits agglutination. Adenosine protects this dehydrogenase in erythrocytes from inactivation by iodoacetate, over the same concentration range in which it enhances agglutination.

Effect of endo-beta-galactosidase on intact human erythrocytes

Endo-beta-galactosidase, a glycosidase that hydrolyzes Gal beta 1-4 GlcNAc linkages in glycoconjugates, has been used to probe the plasma membrane of human erythrocytes. Coomassie blue staining of stroma components separated by sodium dodecyl sulfate-acrylamide gel electrophoresis indicates that treatment of red cells with endo-beta-galactosidase converts Protein 3, the anion transporter of the erythrocyte, to a more compact staining band. No other components detected by Coomassie staining are affected. Following labeling of red cells with galactose oxidase + NaB3H4, 45 to 50% of the [3H]galactose residues can be released by endo-beta-galactosidase. In contrast, only 5% of the label incorporated by treatment with periodate + NaB3H4, can be removed. [3H]Galactose residues are released from three components: Protein 3, Band 4.5, and the megaloglycolipids. The susceptibility of these components to endo-beta-galactosidase, together with the high content of Gal and GlcNAc present in Protein 3 and the megaloglycolipids, suggests that the erythrocyte membrane contains several components with N-acetyllactosamine repeating units, a structure commonly found in connective tissue glycoconjugates.

Distribution of transmembrane polypeptides in freeze fracture

Human erythrocytes have been freeze-fractured, and the polypeptides associated with the separate halves of the membrane bilayer have been analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The transmembrane proteins were differentially separated by the fracture process. Although sialoglycoproteins associated with the outer half of the membrane, the anion transport protein (band 3) mainly remained with the inner half of the membrane. Well-defined fragments of the sialoglycoproteins were produced by the freeze-fracture procedure, indicating that selected covalent bonds of these transmembrane proteins were broken.

Calcium effects on human erythrocyte membrane proteins

The effects of Ca2+ on human erythrocyte membrane proteins were examined by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Ca2+ had several effects on normal human erythrocyte membrane proteins. It affected the binding of cytoplasmic proteins to the membrane, produced a non-reversible aggregation of several membrane proteins and activated apparent proteolysis of membrane proteins. The Ca2+ effect could be obtained with isolated, washed membranes when the erythrocyte cytoplasm was added. These studies indicate that the Ca2+-induced membrane proteolysis and aggregation effects are not due simply to its presence at the time of hemolysis as previously suggested (Carraway, K.L., Triplett, R.B. and Anderson, D.R. (1975) Biochim. Biophys. Acta 379, 571-581), but are the result of more complex interactions between the erythrocyte membrane and cytoplasmic factors.

Lactoperoxidase-catalyzed iodination of horse cytochrome c:monoiodotyrosyl 74 cytochrome c

Iodination of horse cytochrome c with the lactoperoxidase-hydrogen peroxide-iodide system results initially in the formation of the monoiodotyrosyl 74 derivative. This singly modified protein was obtained in pure form by ion exchange chromatography and preparative column electrophoresis. It shows an intact 695 nm absorption band, the midpoint potential of the native protein, a nuclear magnetic resonance spectrum which indicates an undisturbed heme crevice structure, a normal reaction with antibodies directed against native horse cytochrome c, and circular dichroic spectra in which the only changes from those of the native protein can be ascribed to the spectral properties of iodotyrosine itself. This conformationally intact derivative reacts with the succinate-cytochrome c reductase and the cytochrome c oxidase systems of beef mitochondrial particle preparations indistinguishably from the unmodified protein, showing that the region including tyrosine 74 is not involved in these enzymic electron transfer functions of the protein. The circular dichroic spectra of this derivative indicate that the minima observed at 288 and 282 nm in the spectrum of native ferricytochrome c originate from tyrosyl residue 74.

Detection of a variant of protein 3, the major transmembrane protein of the human erythrocyte

A variant of the major transmembrane protein of the human erythrocyte has been detected following proteolytic digestion of intact erythrocytes. Pronase digestion of normal erythrocytes gives rise to a 60,000 molecular weight fragment of Protein 3, while digestion of erythrocytes with the variant protein produces two fragments of 60,000 and 63,000 molecular weight when peptides are separated by sodium dodecyl sulfate-acrylamide gel electrophoresis using the discontinuous buffer system of Laemmli (Laemmli, U. K. (1970) Nature 227, 680-685). The two fragments cannot be resolved if electrophoresis is conducted using the continuous phosphate or Tris/acetate buffer systems. This increased molecular weight of the variant fragment does not appear to be due to increased glycosylation, since neither sialic acid residues nor terminal galactose units can be detected. Furthermore, the transmembrane segment of Protein 3 can be detected after proteolytic digestion at both the external and cytoplasmic membrane surfaces. These transmembrane segments of both the normal and the variant peptide have identical molecular weights of 20,000 to 21,000. These results suggest that the increased molecular weight of the variant peptide is due to the incorporation of an additional segment into that region of the molecule which is exposed at the cytoplasmic side of the membrane.

Localization of thyroid peroxidase and the site of iodination in rat thyroid gland

The iodinated protein was localized in thyroid tissue slices by using radioautography. In unfixed tissue, the labelled protein was localized in the colloid, whereas, in tissue that was fixed before the 125I addition, the label was within the follicular cell. This localizes thyroid peroxidase largely on the endoplasmic reticulum of the cell.

Peroxidase-catalyzed halogenation

Peroxidase-catalyzed halogenation reactions have been established as being important in the biosynthesis of the hormone thyroxine and in biological defense mechanisms. Recently these reactions have been recognized as valuable tools for the study of proteins as well as their arrangement in macromolecular structures. The pathways of peroxidase catalyses can be accommodated within the framework of the classical Chance-George mechanism. This implies that the initial steps of the reaction invariably involve oxidation of peroxidases by peroxides--and that the resulting derivative, compound I, is the oxidant of the halide ions. Such reactions may result either in the formation of hypohalous acids, or in halogenation of the enzyme apoprotein, followed by transhalogenation to substrate for halogenation. Chloro- and myeloperoxidases catalyze oxidation of all halide ions, except F-; oxidation of bromide and iodide is mediated by lactoperoxidase, but horseradish peroxidase only oxidizes iodide. All of the above enzymes except horseradish will oxidize the pseudo halide thiocyanate. The origins of this differentiation remain to be defined, but they presumably reflect significant variation in oxidation potential of different peroxidase-peroxide derivatives, rather than constraints on the peroxidase-donor interactions. As pointed out above, halogenation of the amino acids tyrosine and histidine or these residues in proteins can take place on the enzyme. This makes lactoperoxidase-catalyzed iodination selective. The amino acid residues in proteins that are iodinated depend not only on reactivity of the amino acid residue but also on its geometric location. Thus lactoperoxidase-catalyzed iodination can be a useful tool in the study of protein structure and function. It is also useful in establishing the geometric position of proteins within macromolecular structures. Thyroid peroxidase catalyzes iodination of thyroglobulin and is involved in a second important step, the coupling of the iodotyrosines to form thyroxine or triiodothyronine. A proposed mechanism for this reaction suggests that the oxidation is mediated by the iodoenzyme derivative mentioned above followed by a prototropic rearrangement and scission to form the ether bound of thyronine and a serine residue on thyroglobulin.

Effect of metabolic state on agglutination of human erythrocytes by concanavalin A

Intact freshly drawn or stored human erythrocytes, which show little agglutination by concanavalin A, become agglutinable by this lectin in the presence of adenosine. alpha-Methylglucose (10 mM) completely inhibits this agglutination. The concanavalin A agglutination shows no sensitivity to vinblastine or cytochalasin B. Resealed membranes preparaed with ATP in lysing and resealing medium give modest agglutinability, while the presence of adenosine in both the lysing and the resealing medium results in a substantial agglutinability of the resealed membranes. Mild trypsin treatment of the erythrocytes causes an enhanced sensitivity to adenosine activation of the concanavalin A agglutination, while extensive trypsin treatment produced highly agglutinable erythrocytes that shown no response to the presence of adenosine in the lectin solution. The extensively treated erythrocytes also show concanavalin A agglutination at temperatures below 37 degrees C, under conditions in which intact or moderately treated erythrocytes do not agglutinate, with or without adenosine present. Results suggest that the adenosine activation of concanavalin A agglutination of intact human erythrocytes is mediated through a metabolic conversion of adenosine to a rapidly turned over metabolite which participates directly in the activation of agglutination. The agglutinability does not appear to depend on whole cell ATP levels, but may involve a particular pool of ATP. The effect of variation of cellular metabolic state and the response of particular systems involved in lectin-mediated agglutinability to cellular metabolism seem to be worth consideration in explaining the frequently large differences in agglutinability of und in cells in different biological states, such as those encountered in normal and transformed cells.