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PubMed1988

The structure of the murine Fc receptor for IgG. Assignment of intrachain disulfide bonds, identification of N-linked glycosylation sites, and evidence for a fourth form of Fc receptor.

The Fc receptor (Fc gamma R) of the murine macrophage cell line, J774, was purified by immunoaffinity chromatography then subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and amino-terminal sequencing. FcR material judged to be pure by these criteria was digested with a number of enzymes to identify the cysteine residues engaged in disulfide bonds within the native structure. The results clearly establish that the mouse macrophage Fc gamma R contains two intrachain disulfide bonds, each of which connects adjacent cysteine residues within the two putative extracellular domains of the molecule. In addition, each disulfide-bonded domain was shown to contain two authentic sites of N-linked glycosylation. Extensive peptide sequencing resulted in the unexpected identification of peptide fragments from a fourth Fc gamma R whose sequences were highly homologous to sequences surrounding the two Cys residues in the amino-terminal domain of both alpha and beta 1 Fc gamma R. The fourth Fc gamma R contains a disulfide-bonded amino-terminal domain similar to beta 1 Fc gamma R.

Amino Acid Sequence↗
PubMed1988

Cellular distribution of protein-disulfide interchange enzyme activity in mouse spleen.

In an attempt to precise the cellular distribution of protein-disulfide interchange enzyme activity within different compartments of the splenic lymphoid tissue, we have analyzed the protein-disulfide interchange (PDI) enzyme activity in adherent and nonadherent cell populations of normal and T-cell depleted CBA mice. In vivo depletion of T-cells, as evaluated by functional and cytotoxic tests, was achieved by two i. v. injections of anti-T monoclonal antibodies (Mab F7D5). Nonadherent cell populations were found to have levels of protein-disulfide interchange enzyme activity significantly higher than that of the adherent cells. Pretreatment with F7D5 monoclonal antibodies enhanced the protein-disulfide interchange activity in nonadherent cell population, thus indicating that the major source of the enzyme activity are nonadherent spleen cells, which do not bear T-cell marker, probably B-cells.

Animals↗
PubMed1978

Molecular properties of the adrenergic alpha-receptor. III - Origin of topographical dualism in the reaction of a receptor thiol with symmetrical and unsymmetrical polyamine disulfides.

Structure activity relationship studies previously led to the discovery of two distinct classes of tetramine-disulfides [(I) and (II)] each exhibiting optimum adrenergic alpha-blocking activity. The more potent one (I) was shown to uniquely discriminate between noradrenaline (NA) and adrenaline (A) binding sites. The unusual receptor topographical dualism toward (I) and (II) led to an investigation of the role of structural symmetry in their interaction with the receptor. To this end, a series of unsymmetrical disulfide analogs (x-z) where half of (I) was retained and the other half was made of unsubstituted N-(omega-aminoalkyl)cysteamines [as present in (II) and its homologs] were synthesized and evaluated as alpha-blockers. In addition, the role of the number of basic nitrogens on activity was also examined. It was found that the presence of four nitrogens is necessary for optimum activity. Moreover, it was discovered that optimum alpha-blocking potency is obtained when the respective halves of the two best prototypes (I) and (II) of symmetrical structures are fused [compound (XVI)]. This new unsymmetrical tetramine disulfide has a potency approaching that of (I) and its receptor saturation mechanism is similar. Moreover, it also shares with (I) the ability to discriminate between NA and A elicited responses. The effect of methylation of a single inner nitrogen on potency allowed the conclusion that each half of the unsymmetrical disulfide (XVI) respectively occupy half of the sites for (I) and half of those for (II). Accordingly, the previously observed topographical dualism toward (I) and (II) can best be accommodated by a model where two distinct sets of sites crossing each other over the same receptor thiol are involved. The possible significance of the anionic site multiplicity of the alpha-receptor is briefly discussed.

Adrenergic alpha-Antagonists↗
PubMed1986

The hemoglobins of the bullfrog Rana catesbeiana. The structure of the beta chain of component C and the role of the alpha chain in the formation of intermolecular disulfide bonds.

The adult bullfrog Rana catesbeiana has two major hemoglobin components, B and C. Component C polymerizes by disulfide bond formation between tetramers but component B does not. The amino acid sequence of the first 112 residues of the beta chain of component C has been reported (Baldwin, T. O., and Riggs, A. (1974) J. Biol. Chem. 249, 6110-6118). We have completed the sequence of the beta chain of component C by determining the last 28 residues. This segment contains the 2 cysteinyl residues of the chain. Examination of models indicates that neither of these is in a readily accessible position for the formation of intertetramer disulfide bonds. Reactive sulfhydryl groups of the alpha chains are shown to be responsible for the initial formation of disulfide bonds between tetramers. The beta chains within the tetramers form disulfide bonds only when the hemoglobin molecules are subjected to prolonged incubation at 37 degrees C under oxygen. The beta chains of components B and C appear to be identical; the alpha chains are clearly quite different. This suggests that the alpha B and alpha C subunits interact in the association of the deoxygenated tetramers B and C to form what appears to be a BC2 molecule.

Amino Acid Sequence↗
PubMed1987

New coupling agents for the synthesis of immunotoxins containing a hindered disulfide bond with improved stability in vivo.

Two new coupling agents were synthesized for making immunotoxins containing disulfide bonds with improved stability in vivo: sodium S-4-succinimidyloxycarbonyl-alpha-methyl benzyl thiosulfate (SMBT) and 4-succinimidyloxycarbonyl-alpha-methyl-alpha(2-pyridyldithio)tolue ne (SMPT). Both reagents generate the same hindered disulfide linkage in which a methyl group and a benzene ring are attached to the carbon atom adjacent to the disulfide bond and protect it from attack by thiolate anions. An immunotoxin consisting of monoclonal anti-Thy-1.1 antibody (OX7) linked by means of the SMPT reagent to chemically deglycosylated ricin A-chain had better stability in vivo than an immunotoxin prepared with 2-iminothiolane hydrochloride (2IT) which generates an unhindered disulfide linkage. About 48 h after i.v. injection into mice, one-half of the SMPT-linked immunotoxin present in the blood was in intact form and one-half as released free antibody, whereas equivalent breakdown of the 2IT-linked immunotoxin was seen at about 8 h after injection. Consequently, the blood levels of the SMPT-linked immunotoxin remained higher than those of the 2IT-linked immunotoxin despite loss of immunotoxin from the blood by other mechanisms. Forty-eight h after injection, 10% of the injected dose of the SMPT-linked immunotoxin remained in the bloodstream as compared with only 1.5% of the 2IT-linked immunotoxin. The ability of immunotoxins prepared with the new reagents to inhibit protein synthesis by Thy-1.1-expressing AKR-A/2 lymphoma cells in vitro was identical to that of immunotoxins prepared with 2IT or N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). Clonogenic assays showed that fewer than 0.01% of AKR-A/2 cells survived exposure to high concentrations of OX7-abrin A-chain immunotoxins prepared with SMBT, 2IT, or SPDP. Twelve clones of cells which had survived treatment with the SMBT-linked immunotoxin were isolated. None of the clones was selectively resistant to the SMBT-linked immunotoxin when retested in cytotoxicity assays. In conclusion, immunotoxins prepared with the new coupling agents should have improved antitumor activity in vivo because they are longer lived and do not break down so readily to release free antibody which could compete for the target antigens.

Animals↗
PubMed1986

Binding of the glucocorticoid receptor to the rat liver nuclear matrix. The role of disulfide bond formation.

The nuclear matrix is a putative skeletal structure which has been implicated in many nuclear functions. To assess a possible role of the nuclear matrix in glucocorticoid action, purified rat liver nuclei containing glucocorticoid-receptor complexes were treated with DNase I +/- RNase A followed by 1.6 M NaCl, thus yielding salt-extractable and salt-resistant (nuclear matrix) fractions. The subnuclear distribution of hormone-receptor complexes was determined by following the fate of unmetabolized radiolabel after injection of labeled triamcinolone acetonide into adrenalectomized animals and subjecting various subfractions to immunoblotting using a monoclonal antibody which recognizes the glucocorticoid receptor. Both techniques indicated that 50-70% of the total nuclear hormone-receptor complexes were recovered in the nuclear matrix fraction. Previous results (Kaufmann, S. H., and Shaper, J. H. (1984) Exp. Cell Res. 155, 477-495) suggest that a variety of nuclear polypeptides become nuclease- and salt-resistant as a result of the formation of intermolecular disulfide bonds. The following evidence suggests that disulfide bonds mediate the association between the glucocorticoid receptor and the nuclear matrix. When nuclei were isolated in the absence of sulfhydryl-blocking and -cross-linking reagents, sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions revealed that the receptor was present as a high molecular weight disulfide-cross-linked complex. When nuclei were isolated in the presence of the irreversible sulfhydryl-blocking reagent iodoacetamide, the disulfide bonds which cross-linked the receptor into high molecular weight complexes were absent; and 85-100% of the hormone-receptor complexes were salt-extractable. When nuclei (isolated in the absence of iodoacetamide) were treated with the sulfhydryl-cross-linking reagent sodium tetrathionate, greater than 95% of the nuclear hormone-receptor complexes became resistant to extraction with nucleases and 1.6 M NaCl. The implications of these results for other matrix-associated nuclear functions are discussed.

Animals↗
PubMed1987

Bovine high molecular weight kininogen. The amino acid sequence, positions of carbohydrate chains and disulfide bridges in the heavy chain portion.

The existence of two types of circulating bovine plasma high molecular weight kininogen (HMWK) was predicted from analyses of complementary DNAs coding for this protein (Kitamura, N., Takagaki, Y., Furuto, S., Tanaka, T., Nawa, H., and Nakanishi, S. (1983) Nature 305, 545-549). The present protein-based study provided evidence in support of the proposed amino acid sequence derived from analysis of the cDNA clone, and the results confirm the existence of two types of circulating HMWK. Type I HMWK contains a heavy chain composed of 361 residues, while the heavy chain of type II HMWK contains 359 residues. The amino acid sequences of type I and type II HMWK determined in this study were identical to that inferred from the cDNA sequence with the exception of microheterogeneity observed in the cDNA at position 87 (Glu/Gln) and 168 (Lys/Arg). The heavy chain of type I HMWK contains 4 asparagine-linked carbohydrate chains at Asn-69, -150 (or -151), -179, and -186, while the heavy chain of type II HMWK contains these and an additional carbohydrate chain at Asn-264. In addition, a carbohydrate chain was found to be O-glycosidically linked to Thr-118 in both chains. Among nine disulfide linkages found in HMWK, eight intrachain disulfide pairs were established in the heavy chain. One interchain disulfide bridge occurs between the heavy chain and the light chain. This disulfide pairing, as well as repeating amino acid sequences observed in the heavy chain, provides strong evidence for the existence of three homologous domains in the heavy chain of bovine HMWK.

Amino Acid Sequence↗
PubMedDate not supplied

Purge and trap method for determination of volatile halocarbons and carbon disulfide in table-ready foods.

A method developed for the determination of ethylene dibromide in table-ready foods has been modified and expanded to include 7 other volatile halocarbons and carbon disulfide. Samples are stirred with water and purged with nitrogen for 0.5 h in a water bath at 100 degrees C. The analytes collected on a duplex trap composed of Tenax TA and XAD-4 resin are eluted with hexane and determined by gas chromatography with electron capture detection or Hall electrolytic conductivity detection. Flame photometric detection in the sulfur mode is used to determine carbon disulfide. Thick-film, wide-bore capillary columns are used exclusively in both the determination and confirmation of the halogenated analytes. The higher levels of analytes are also confirmed by full scan gas chromatography mass spectrometry (GC/MS). Samples are analyzed for carbon disulfide, methylene chloride, chloroform, 1,2-dichloroethane, methyl chloroform, carbon tetrachloride, trichloroethylene, 1,2-dibromoethane, and tetrachloroethylene. Initially, 19 table-ready foods from the Food and Drug Administration's Total Diet Study were analyzed by this method. A limited survey of those food items exhibiting high levels of analytes was conducted. Samples exhibited levels up to 3300 ppb (methyl chloroform in Parmesan cheese). Recoveries of all 9 analytes from fortified samples ranged from 83 to 104%. Chromatograms from this purge and trap method are clean, enabling quantitation levels of low parts per billion and sub-parts per billion to be achieved for the halogenated analytes. The quantitation limit for carbon disulfide is 12 ppb. Two compounds found in drinking water were identified by GC/MS as bromodichloromethane and chlorodibromomethane. Drinking water from several cities was analyzed for these trihalomethanes as well as for bromoform. Levels of up to 17 ppb bromodichloromethane were found. Recoveries ranged from 96 to 103%.

Carbon Disulfide↗
PubMed1985

The biosynthesis of rat transferrin. Evidence for rapid glycosylation, disulfide bond formation, and tertiary folding.

The transit time of newly synthesized transferrin in the liver is markedly longer than that of albumin. We sought to learn the basis of this difference by the use of labeled leucine and mannose in vivo and by isolation of newly formed transferrin from rough microsomes of rat liver. Albumin and alpha 1-antitrypsin, a second glycoprotein, were also studied for comparison. Minimal hepatic transit times were 17, 23, and 31 min for albumin, alpha 1-antitrypsin, and transferrin, respectively. The delay in the case of transferrin was found to occur chiefly in the rough endoplasmic reticulum and to be paralleled by an increase in the amount of transferrin relative to albumin in that organelle. Initial glycosylation of transferrin was as rapid as that of alpha 1-antitrypsin, and essentially all of the transferrin in the rough endoplasmic reticulum contained glycans which bound to concanavalin A and were removed by endoglycosidase H. Only 3% of the transferrin isolated from the rough microsomes came from the plasma by endocytosis or adsorption. Rapidity of disulfide bond formation in rough microsomes was evident from the presence of only 1.3 cysteine thiols/molecule of rough microsomal transferrin (total of 19 cystines) and the absence of mixed disulfides. Peptide patterns upon mild proteolysis were consistent with a native configuration of disulfide bond pairing. The ability of rough microsomal transferrin to bind and deliver iron through interaction with transferrin receptors on reticulocytes suggests that considerable tertiary structure is present. Thus, initial glycosylation, disulfide bridging, and tertiary folding are all rapid processes. The cause for the slow release of transferrin from the rough endoplasmic reticulum may lie with a rate-limiting transfer mechanism.

Animals↗
PubMed1985

Inhibition of mammalian 5-lipoxygenase by aromatic disulfides.

As a primary step in leukotriene biosynthesis, arachidonic acid is converted into 5-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid by 5-lipoxygenase. This enzyme is studied in the supernatant fraction from sonified RBL-1 cells, a preparation that converts [1-14C]arachidonic acid to 5-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid and several 5,12-dihydroxyeicosatetraenoic acids including LTB4. In order to examine the reversibility of inhibitors, the supernatant fraction can be depleted of low molecular weight constituents by vacuum filtration. The 5-lipoxygenase is irreversibly inhibited by 500 microM N-ethyl-maleimide or 300 microM methyl methanethiolsulfonate, reagents that react covalently with protein sulfhydryl groups. In contrast, diphenyl disulfide reversibly inhibits this enzyme at 1-5 microM, irrespective of the GSH concentration in the supernatant. KCN also inhibits 5-lipoxygenase at 4 mM, suggesting the presence of a metal-containing prosthetic group. These observations imply that diphenyl disulfide and similar molecules with electron-releasing substituents on the aromatic rings could inhibit by binding to an electrophilic metallic center, the binding being stabilized by hydrophobic interactions between the enzyme and the aromatic groups on the flexible disulfide. Even though diphenyl disulfide does not inhibit soybean 15-lipoxygenase or endoperoxide synthase in cell-free systems, this compound does suppress prostaglandin as well as leukotriene synthesis in intact murine peritoneal macrophages and CXBG cells. Since lipoxygenases are susceptible to peroxide activation and peroxidase deactivation, changes in the redox state of the cell may alter arachidonic acid metabolism as effectively as actual enzyme inhibition.

Animals↗
PubMed1985

The molecular morphology of bovine heart mitochondrial NADH----ubiquinone reductase. Native disulfide-linked subunits and rotenone-induced conformational changes.

Bovine heart mitochondrial NADH----ubiquinone reductase (complex I), contains two disulfide-linked subunits of 75 and 33 kDa as revealed by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis with beta-mercaptoethanol omitted from preparation of the sample for the first dimension. Two unidentified polypeptides (110-115 and 69 kDa) are also found in disulfide linkage with the two complex I subunits. The 110-115-kDa polypeptide appears to be pyridine dinucleotide transhydrogenase by several criteria including selective precipitation with an antibody raised to the purified transhydrogenase. The two disulfide-linked subunits were also found in a product cross-linked for 2 min with dithiobis (succinimidyl propionate) (DSP) along with five other complex I subunits of 53-57, 42, 24-27, 17-18, and 12.5-15.5 kDa (Gondal, J.A., and Anderson, W.M. (1985) J. Biol. Chem. 260, 5931-5935) indicating that these seven subunits lie within 11-12 A of each other at one or more points in space in the enzyme's interior. Cross-linking of complex I with DSP for 2 min in the presence of 1 microM rotenone yielded a cross-linked product consisting of the two natural disulfide-linked subunits and the 110-115- and 69-kDa polypeptides. This suggests that rotenone induces a conformational change in the enzyme that moves the seven DSP cross-linked subunits away from each other and outside the 11-12 A bridging distance of DSP. This alteration in conformation may be communicated to iron-sulfur center N-2 within the hydrophobic outer shell of the enzyme to prevent electron transfer to its natural electron acceptor, ubiquinone. A model of rotenone action based upon these observations is presented.

Animals↗
PubMedDate not supplied

[Action of pyridoxine on lipid metabolism in carbon disulfide-poisoned rats].

The author studied the influence of pyridoxine (8 mg/kg bw) on upset lipid metabolism in rats exposed to carbon disulfide (30 mg/m3) inhalation over 90 days. The content of total lipids, total esterified and free cholesterol, free fatty acids, phospholipids, triglycerides and beta-lipoproteins was measured in serum on days 15, 30 and 90 since exposure. Carbon disulfide alone caused a reduction in the level of some lipid groups on day 15, whereas on days 30 and 90 it provokes an elevation of the content of total fats and all lipid groups under study. Administration of pyridoxine alone brought about a decrease in lipid characteristics. The combined use of the vitamin and carbon disulfide made these characteristics return to normal. Pyridoxine is a possible active factor in the prophylaxis of atherosclerotic lesions in carbon disulfide poisoning.

Animals↗
PubMed1978

Keratin filaments of cultured human epidermal cells. Formation of intermolecular disulfide bonds during terminal differentiation.

Human epidermal cells grown in culture synthesize abundant keratins. These keratins are similar to those of stratum corneum of human epidermal callus in their insolubility in dilute aqueous buffers, their molecular weight range of 40,000 to 60,000, their immunolgical reactivity, and their ability to assemble into 80 A tonofilaments in vitro; but there are differences in the molecular weights of some of the proteins, the number of components, and their charge heterogeneity, related at least in part to phosphorylation. About 30% of all the proteins of living cultured keratinocytes consists of keratins, compared with over 85% of stratum corneum. All the keratins of human stratum corneum were found to be cross-linked by intermolecular disulfide bonds while most keratins of the living cells were not. As the cells mature in Methocel-stabilized suspension culture, their keratins become increasingly disulfide cross-linked. When uncross-linked tonofilaments of living keratinocytes are dissolved in 8 M urea and the filaments reconstituted in vitro their keratins become disulfide cross-linked under aerobic conditions and consequently insoluble in solutions of 8 M urea or sodium dodecyl sulfate. The results indicate that the uncross-linked state of the keratins in living cells is due to the reducing intracellular environment and not to a precursor state related to the primary structure of the proteins. The disulfide cross-links stabilizing the keratin filaments must be distinguished from the epsilon-(gamma-glutamyl)lysine cross-links stabilizing the cornified cell envelope.

Cell Differentiation↗
PubMed1978

[Molecular ageing in bovine plasma albumin I. Exposure of disulfide bonds in the N-B transition (author's transl)].

An accessibility of the disulfide bonds of defatted SH-blocked bovine plasma albumin (BPA) to reduction by dithiothreitol was studied at 4 degree C. Upon reduction SH-blocked BPA acquired one SH per mole in the pH range from 4.0 to 6.0. Above pH 6.5 (the pH range of the N-B transition) an increasing number of the disulfide bonds became susceptible to reduction by dithiothreitol. Chemicals, such as KC1, fatty acid, sodium dodecylsulfate which suppress the structural fluctuation of BPA in the alkaline region decreased the accessibility of the disulfide bonds to reduction. The conversion of buried disulfide bonds into exposed ones is interpreted as being due to conformational changes in the N-B transition (pH 7.0 approximately 9.0).

Animals↗
PubMed1984

Primary structure of human alpha 2-macroglobulin. III. Primary structure of three large disulfide-bridged CNBr fragments, located in the COOH-terminal part of alpha 2-macroglobulin and accounting for 301 residues.

The amino acid sequences have been determined for three CNBr fragments of human alpha 2-macroglobulin which form a disulfide-bridged Mr = 40,000 fragment set. The fragments are located in the COOH-terminal part of alpha 2-macroglobulin (CB18, residues 776-936; CB23, residues 1292-1355; and CB26, residues 1376-1451). CB18 contains one glucosamine-based carbohydrate group attached to Asn-71 and two internal disulfide bridges (Cys-23 bound to Cys-51 and Cys-49 bound to Cys-85, respectively). Cys-123 is disulfide bridged to Cys-7 of CB23. Cys-38 of CB23 is disulfide bridged to Cys-69 of CB26. CB26, which contains one glucosamine-based carbohydrate group attached to Asn-26, is the COOH-terminal CNBr fragment. CB18, CB23, and CB26 account for 301 of the 1451 residues of the subunit of alpha 2-macroglobulin.

Amino Acid Sequence↗
PubMed1983

Specific mixed disulfide formation with purified bovine cardiac glycogen synthase I and glutathione.

Bovine cardiac glycogen-free glycogen synthase I reacts with oxidized glutathione at low temperature to partially inactivate the enzyme. Evidence is presented that a mixed disulfide between glutathione and the enzyme is formed in this reaction. A short incubation of the GSSG-treated enzyme with dithiothreitol restores full enzyme activity. The reaction with GSSG is pH dependent and the product is quite stable at neutral pH. Oxidation of one sulfhydryl group in glycogen synthase is associated with a loss of 60-70% of the enzyme activity. Further modification of protein sulfhydryls has less effect on the enzyme activity. Other low molecular weight disulfides also inactivate glycogen synthase and treatment with [35S]cystine to produce a 40% loss of enzyme activity gave rise to a single major radioactive peptide after cyanogen bromide digestion. Thus the GSSG-mediated inactivation of glycogen synthase apparently occurs through a single reactive sulfhydryl group that forms a mixed disulfide with low molecular weight disulfide molecules. Uridine 5'-diphosphate glucose and glycogen prevent the inactivation of glycogen-free glycogen synthase with GSSG, and glucose 6-phosphate retards the rate of inactivation. Reduction and reactivation of the GSSG-oxidized glycogen synthase is not affected by glycogen and it occurs readily at neutral pH with dithiothreitol, mercaptoethanol, or cysteamine. Oxidation of the reactive sulfhydryl group with GSSG has no effect on the rate of glycogen synthase phosphorylation by the catalytic subunit of cAMP-dependent protein kinase.

Binding Sites↗
PubMed1983

[Disulfide reductase activity in mouse regenerating liver].

Fourteen hours after partial hepatectomy there was a decrease in basal disulfide reductase and glutathione reductase activity in cytosole fraction of proliferating hepatocytes. In nuclear fraction, the activation effect of cAMP and cGMP on the disulfide recovery was replaced by inhibition. Meanwhile the activity of glutathione reductase noticeably increased. Forty-five hours after operation disulfide reductase activity of cytosole appreciably rose during maximal mitotic activity of the regenerating liver. The data obtained provide evidence in favor of the involvement of disulfide reductase enzymes into reparative regeneration of the liver.

Animals↗
PubMed1984

Induced interchain disulfide bonding in cAMP-dependent protein kinase II.

Cupric phenanthroline was used to catalyze the formation of disulfide bonds in cAMP-dependent protein kinase II. Incubation of holoenzyme alone with cupric phenanthroline resulted in no disulfide bond formation. In contrast, when holoenzyme was preincubated with cAMP prior to treatment with cupric phenanthroline, specific interchain disulfide bonding was found between the regulatory (R) and catalytic (C) subunits. Formation of the R-C dimer was independent of the phosphorylation state of R. Experiments with R that had been freed of bound cyclic nucleotide suggest that a ternary complex of R, C, and cAMP is necessary for the formation of this cross-linked species. When the dimeric R-subunit alone was incubated with cupric phenanthroline, the two protomers of the R-dimer were frequently cross-linked. Phosphorylation of R did not affect the formation of R-R dimers. In contrast to the R-subunit of the type I protein kinase, R-R dimers of the type II protein kinase were not normally observed in the absence of an added catalyst. Factors which favor disulfide bond formation in the R-dimer have not been determined.

Animals↗