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Sillerud LO, Han CH, Bitensky MW, Francendese AA. Metabolism and structure of triacylglycerols in rat epididymal fat pad adipocytes determined by 13C nuclear magnetic resonance. J Biol Chem 1986. [DOI: 10.1016/s0021-9258(17)38512-5] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Hildebrandt JD, Codina J, Rosenthal W, Birnbaumer L, Neer EJ, Yamazaki A, Bitensky MW. Characterization by two-dimensional peptide mapping of the gamma subunits of Ns and Ni, the regulatory proteins of adenylyl cyclase, and of transducin, the guanine nucleotide-binding protein of rod outer segments of the eye. J Biol Chem 1985; 260:14867-72. [PMID: 3932359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Ns and Ni, the regulatory proteins affecting adenylyl cyclase, and transducin, the guanine nucleotide-binding protein from rod outer segments of the eye, are structurally and functionally related proteins. Of these, the alpha subunits are between 39 and 42 kDa in mass, beta subunits are all of 35 kDa in mass, and gamma subunits are much smaller, of approximately 5-8 kDa in mass. We compared, by two-dimensional peptide mapping of iodinated peptides, the beta and gamma subunits of human erythrocyte Ns, human erythrocyte Ni, the beta gamma complex derived from purification of bovine brain N proteins, and frog and bovine eye transducins. We found that gamma subunits in human erythrocyte Ns and Ni and in bovine brain beta gamma complex are indistinguishable by this approach. In contrast, gamma subunits associated with frog and bovine transducin differed markedly between each other and from N protein-associated gamma. beta subunits, on the other hand, yielded essentially indistinguishable peptide maps regardless of whether derived from N proteins or from transducin and regardless also of species of origin: human versus bovine versus frog. These results suggest that the gamma subunit may impart functional heterogeneity of this family of proteins which is evident in the N proteins on the one hand and the transducin proteins on the other.
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Hildebrandt JD, Codina J, Rosenthal W, Birnbaumer L, Neer EJ, Yamazaki A, Bitensky MW. Characterization by two-dimensional peptide mapping of the gamma subunits of Ns and Ni, the regulatory proteins of adenylyl cyclase, and of transducin, the guanine nucleotide-binding protein of rod outer segments of the eye. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(17)38653-2] [Citation(s) in RCA: 91] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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29
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Rasenick MM, Wheeler GL, Bitensky MW, Kosack CM, Malina RL, Stein PJ. Photoaffinity identification of colchicine-solubilized regulatory subunit from rat brain adenylate cyclase. J Neurochem 1984; 43:1447-54. [PMID: 6436438 DOI: 10.1111/j.1471-4159.1984.tb05407.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Five GTP binding proteins in rat cerebral cortex synaptic membranes were identified by photoaffinity labelling with [3H] or [32P](P3-azido-anilido)-P1-5' GTP (AAGTP). When AAGTP-treated membranes were incubated with colchicine or vinblastine and subsequently washed, a single AAGTP-labelled protein of 42 kD was released into the supernatant. About 30% of the total labelled 42-kD protein was released into supernatants from membranes pretreated with colchicine or vinblastine compared with 15% released from control membranes. The amount of adenylate cyclase regulatory subunit (G unit) remaining in these membranes was assessed with reconstitution studies after inactivating the adenylate cyclase catalytic moiety with N-ethylmaleimide (NEM). Forty to fifty percent of functional G units were lost from membranes treated with colchicine prior to washing. This 40-50% loss of functional G unit after colchicine treatment corresponds to the previously observed 42% loss of NaF and guanylyl-5'-imidodiphosphate [Gpp(NH)p]-activated adenylate cyclase. Release of the AAGTP-labelled 42-kD protein from colchicine-treated synaptic membranes is double that from lumicolchicine-treated membranes. This colchicine-mediated release of 42-kD protein correlates with a doubling of functional G unit released from synaptic membranes after colchicine treatment. These findings suggest multiple populations of the G unit within the synaptic plasma membrane, some of which may interact with cytoskeletal components.
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Halliday KR, Stein PJ, Chernoff N, Wheeler GL, Bitensky MW. Limited trypsin proteolysis of photoreceptor GTP-binding protein. Light- and GTP-induced conformational changes. J Biol Chem 1984; 259:516-25. [PMID: 6323413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The amphibian photoreceptor rod outer segment contains a guanine nucleotide-binding complex which consists of a 39,000-dalton polypeptide that binds guanine nucleotides (G protein), a 36,000-dalton polypeptide (H protein), and an approximately 6,500-dalton polypeptide. Sensitivity to trypsin proteolysis was utilized as a probe of structure-function relationships for these polypeptides. Digestion of the H protein generated fragments of 26,000 and 15,000 daltons whose proteolytic susceptibility was not altered by guanosine triphosphates, light, or membranes. The approximately 6,500-dalton polypeptide was not trypsin sensitive. When the G protein was eluted from illuminated membranes by GTP, trypsin proteolysis cleaved a terminal 1,000-dalton fragment (G1) to yield a 38,000-dalton fragment (G38). With increased digestion time, a 6,000-dalton fragment (G6) was removed from G38 to yield a 32,000-dalton fragment (G32). G32 was subsequently digested to fragments of 23,000 and 12,000 daltons. However, when the G protein was eluted from illuminated membranes by hydrolysis-resistant analogues of GTP, G32 was protected from further digestion. This is consistent with a GTP-induced conformational change in the G protein which is altered by GTP hydrolysis. Proteolysis of the G protein after covalent labeling with a photoaffinity analogue of GTP demonstrated that the analogue is bound to first G38 and then G32, indicating the GTP-binding site is associated with G32. Fragment G6 was cleaved when the G protein was soluble or bound to unilluminated membranes. However, when bound to illuminated membranes, fragments were generated reflecting the loss of 7,500, 9,000, or 11,000 daltons from the G protein. This light-induced alteration in proteolytic susceptibility indicates there is a light-induced conformational change in the G protein. Fragment G1 was not removed from the G protein when it was membrane bound, suggesting G1 is involved in binding to a membrane structure. These data suggest that the light-induced binding of the G protein to illuminated membranes and the reversal of this binding by GTP are mediated through conformational changes in the G protein and that three conformations exist: 1) a basal, inactive conformation; 2) a primed conformation induced by binding to photolyzed rhodopsin, with a high affinity for GTP; and 3) an active conformation, induced by binding of GTP, which activates the catalytic complex of light-activated phosphodiesterase.
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Halliday KR, Stein PJ, Chernoff N, Wheeler GL, Bitensky MW. Limited trypsin proteolysis of photoreceptor GTP-binding protein. Light- and GTP-induced conformational changes. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)43692-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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32
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Yamazaki A, Stein PJ, Chernoff N, Bitensky MW. Activation mechanism of rod outer segment cyclic GMP phosphodiesterase. Release of inhibitor by the GTP/GTP-binding protein. J Biol Chem 1983; 258:8188-94. [PMID: 6305976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The physiological regulation of light-activated cyclic GMP phosphodiesterase (EC 3.1.4.17) in rod outer segments has been shown to depend upon a heat-stable inhibitor and upon the reversal of its effect by a specific GTP/GTP-binding protein complex (Hurley, J. B. (1980) Biochem. Biophys. Res. Commun. 92, 505-510; Yamazaki, A., Bartucca, F., Ting, A., and Bitensky, M. W. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 3702-3706). Washing of illuminated disc membranes with an isotonic buffer released 86% of the peripheral proteins without any release of inhibitor. Subsequent washing with the same isotonic buffer containing GTP released 80% of the inhibitor. When inhibitor was eluted with guanosine-5'-(beta, gamma-imino)triphosphate, it had an apparent molecular weight of 60,000 on Sephadex G-100. The release of inhibitor by guanosine-5'-(beta, gamma-imino)triphosphate was also demonstrated with sucrose density gradient centrifugation. Inhibitor release from the disc membrane by GTP or its analogue was accompanied by the release of the GTP-binding protein and an increased phosphodiesterase activity in the membrane. However, following GTP hydrolysis, both inhibitor and GTP-binding protein returned to the membrane and phosphodiesterase activity in the membrane decreased proportionally. In contrast, incubation of disc membranes with guanosine-5'-(beta, gamma-imino)-triphosphate produced an increase of inhibitor activity in the supernatant and an increase of phosphodiesterase activity in the pellet which remained constant after the initial increase. These data clearly show that the activation of phosphodiesterase by the GTP/GTP-binding protein complex resulted from the release of inhibitor. Hydrolysis of GTP resulted in the reassociation of inhibitor with and concomitant inhibition of disc membrane phosphodiesterase.
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Yamazaki A, Stein PJ, Chernoff N, Bitensky MW. Activation mechanism of rod outer segment cyclic GMP phosphodiesterase. Release of inhibitor by the GTP/GTP-binding protein. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(20)82047-x] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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34
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Menkes DB, Rasenick MM, Wheeler MA, Bitensky MW. Guanosine triphosphate activation of brain adenylate cyclase: enhancement by long-term antidepressant treatment. Science 1983; 219:65-7. [PMID: 6849117 DOI: 10.1126/science.6849117] [Citation(s) in RCA: 116] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Activation of adenylate cyclase by a stable guanosine 5'-triphosphate analog was augmented in brain membrane preparations from rats treated on a long-term basis with tricyclic antidepressants or electroconvulsive shock. These treatments may facilitate cyclase activation by promoting the interaction of the regulatory and catalytic subunits of the enzyme. This finding suggests a possible mechanism for the changes in sensitivity to various neurotransmitters seen after antidepressant administration.
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35
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Williams SK, Howarth NL, Devenny JJ, Bitensky MW. Structural and functional consequences of increased tubulin glycosylation in diabetes mellitus. Proc Natl Acad Sci U S A 1982; 79:6546-50. [PMID: 6959136 PMCID: PMC347164 DOI: 10.1073/pnas.79.21.6546] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The extent of in vitro nonenzymatic glycosylation of purified rat brain tubulin was dependent on time and glucose concentration. Tubulin glycosylation profoundly inhibited GTP-dependent tubulin polymerization. Electron microscopy and NaDodSO4/polyacrylamide gel electrophoresis showed that glycosylated tubulin forms high molecular weight amorphous aggregates that are not disrupted by detergents or reducing agents. The amount of covalently bound NaB3H4-reducible sugars in tubulin recovered from brain of streptozotocin-induced diabetic rats was dramatically increased as compared with tubulin recovered from normal rat brain. Moreover, tubulin recovered from diabetic rat brain exhibited less GTP-induced polymerization than tubulin from nondiabetic controls. The possible implications of these data for diabetic neuropathy are discussed.
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36
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Bitensky MW, Wheeler MA, Rasenick MM, Yamazaki A, Stein PJ, Halliday KR, Wheeler GL. Functional exchange of components between light-activated photoreceptor phosphodiesterase and hormone-activated adenylate cyclase systems. Proc Natl Acad Sci U S A 1982; 79:3408-12. [PMID: 6285349 PMCID: PMC346429 DOI: 10.1073/pnas.79.11.3408] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Previous studies have noted profound similarities between the regulation of light-activated 3',5'-cyclic nucleotide phosphodiesterase (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) in retinal rods and hormone-activated adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in a variety of tissues. We report here the functional exchange of components isolated from the photoreceptor system, which displayed predicted functional characteristics when incubated with recipient adenylate cyclase systems from rat cerebral cortical and hypothalamic synaptic membranes and frog erythrocyte ghosts. We demonstrate functional exchange of photoreceptor components at each of three loci: the hormone receptor, the GTP-binding protein (GBP), and the catalytic moiety of adenylate cyclase. Illuminated (but not unilluminated) rhodopsin was fund to mimic the hormone-receptor complex, causing GTP-dependent activation of adenylate cyclase. The photoreceptor GBP complexed with guanosine 5'-[beta, gamma)imidotriphosphate (p[NH]ppG) produced a marked activation of recipient adenylate cyclase systems. Much smaller activation was observed when GBP was not complexed with p[NH]ppG. A heat-stable photoreceptor phosphodiesterase inhibitor reduced both basal and Mn2+-activated adenylate cyclase activities and this inhibition was reversed by photoreceptor GBP.p[NH]ppG. These data demonstrate a remarkable functional compatibility between subunits of both systems and furthermore imply that specialized peptide domains responsible for protein-protein interactions are highly conserved.
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37
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Yamazaki A, Bartucca F, Ting A, Bitensky MW. Reciprocal effects of an inhibitory factor on catalytic activity and noncatalytic cGMP binding sites of rod phosphodiesterase. Proc Natl Acad Sci U S A 1982; 79:3702-6. [PMID: 6285360 PMCID: PMC346494 DOI: 10.1073/pnas.79.12.3702] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
In illuminated rod outer segment membranes, GTP and guanosine 5'-[beta, gamma-imido]triphosphate (p[NH]ppG) have reciprocal effects on cGMP phosphodiesterase (PDEase; 3':5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) activity and cGMP binding to noncatalytic sites on that enzyme. Two micromolar p[NH]ppG increased PDEase activity more than 2-fold while inhibiting cGMP binding more than 40%. Reduction of noncatalytic cGMP binding, which followed addition of p[NH]ppG, was not a result of PDEase activation. Both effects of p[NH]ppG were completely dependent on the presence of bleached rhodopsin. A heat-stable factor has been found to inhibit PDEase activity and also to stimulate cGMP binding to noncatalytic cGMP binding sites. Addition of p[NH]ppG reversed the effects of this factor on both PDEase activity and cGMP binding. During purification of this material, the activity peaks for both PDEase inhibition and activation of noncatalytic cGMP binding comigrated on both Blue Sepharose CL-6B column chromatography and sucrose density gradients centrifugation, suggesting that the same factor could be responsible for both inhibition of PDEase activity and enhancement of noncatalytic cGMP binding. Limited tryptic proteolysis of PDEase, which markedly reduced cGMP binding to the noncatalytic sites, and experiments using highly purified cAMP (free of cGMP) as substrate for PDEase showed that the binding of cGMP to noncatalytic sites was not required for the heat-stable inhibitory factor to inhibit PDEase activity. We discuss possible relationships between the regulation of PDEase and the binding of cGMP to noncatalytic sites.
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38
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Wheeler M, Tishler M, Bitensky MW. Agaridoxin: a fungal catecholamine which acts as an alpha 1 agonist of mammalian hypothalamic adenylate cyclase. Brain Res 1982; 231:387-98. [PMID: 6120025 DOI: 10.1016/0006-8993(82)90375-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Agaridoxin, a catecholamine isolated from mushrooms, and 4 synthetic analogues cause activation of adenylate cyclase in the presence of guanylyl imidodiphosphate (Gpp(NH)p) in membrane particles prepared from rat hypothalamus. These compounds also activate adenylate cyclase preparations from rat kidney, liver and cerebral cortex. In the presence of tyrosinase, these compounds are readily oxidized to quinones which lack agonist activity. Studies with selective adrenergic blockers suggest that agaridoxin acts at an alpha 1-type receptor. Agaridoxin-mediated adenylate cyclase stimulation is most effectively antagonized by WB-4101 and phenoxybenzamine, while propranolol and yohimbine are without inhibitory effect. Agaridoxin and the alpha 1 agonist methoxamine inhibited the binding of [3H]WB-4101 in rat hypothalamic and cerebral cortical membranes. The values of Ki for both compounds are lower than that of norepinephrine. The agaridoxin analogue, 4-aminocatechol hydrochloride, is a more effective and potent adenylate cyclase activator than agaridoxin or methoxamine.
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39
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Yamazaki A, Miki N, Bitensky MW. Purification and characterization of a light-activated rod outer segment phosphodiesterase. Methods Enzymol 1982; 81:526-32. [PMID: 6285126 DOI: 10.1016/s0076-6879(82)81073-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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40
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Rasenick MM, Stein PJ, Bitensky MW. The regulatory subunit of adenylate cyclase interacts with cytoskeletal components. Nature 1981; 294:560-2. [PMID: 7312044 DOI: 10.1038/294560a0] [Citation(s) in RCA: 123] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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41
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Shinozawa T, Bitensky MW. Purification and characteristics of photoreceptor light-activated guanosinetriphosphatase. Biochemistry 1981; 20:7068-74. [PMID: 6119110 DOI: 10.1021/bi00528a003] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We describe a reconstitution of light-activated vertebrate photoreceptor GTPase and a purification of the GTP-binding protein (G protein), which is a component of the GTPase and modulates the light-activated phosphodiesterase (PDE) enzyme system. Rod outer segments (ROS) of bull frogs were treated with ethylenediaminetetraacetic acid (EDTA), and the GTPase and PDE fractions were solubilized (EDTA supernatant). When the EDTA supernatant and EDTA-treated membrane fraction (EDTA-washed membranes) were recombined, light-dependent GTPase activity appeared. In the reconstituted system, the Km for GTP as substrate was 0.5 microM; the optimum pH was 7.5-8.0. The isoelectric point of GTPase in EDTA supernatant was 4.8. G protein was purified 400-fold from ROS, and the molecular weight of G protein was determined to be 40 000 by polyacrylamide gel electrophoresis. The amount of G protein in ROS was calculated as at least 1 molecule per 400 rhodopsin molecules. By recombining (in the presence or absence of GTP) purified G protein, PDE, H fraction (an additional component of GTPase), and illuminated or unilluminated EDTA-washed membranes (as a source of rhodopsin), we showed that illuminated rhodopsin, G protein, PDE, and GTP are the minimum requirements for light-dependent PDE activity. We discuss the significance of these findings in the regulation of the light-activated GTPase and PDE activities, especially with regard to the mechanism of activation.
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42
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Williams SK, Devenny JJ, Bitensky MW. Micropinocytic ingestion of glycosylated albumin by isolated microvessels: possible role in pathogenesis of diabetic microangiopathy. Proc Natl Acad Sci U S A 1981; 78:2393-7. [PMID: 6941299 PMCID: PMC319352 DOI: 10.1073/pnas.78.4.2393] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Microvessels isolated from rat epididymal fat exhibit differential vesicular ingestion rates for unmodified and non-enzymatically glycosylated rat albumin. While unmodified rat albumin is excluded from ingestion by endothelial micropinocytic vesicles, glycosylated albumin is avidly taken up by endocytosis. Interaction of albumin and glycosylated albumin with endothelium was studied with a double-label fluorescence assay of micropinocytosis. When glycosylated albumin was present at a concentration of 6% with respect to total albumin (the level found in "non diabetic" serum), only glycosylated albumin was ingested. At higher concentrations of glycosylated albumin (those found in diabetic serum), both albumin and glycosylated albumin are ingested. Glycosylation of endothelial membrane components results in stimulated ingestion of glycosylated albumin, persistent exclusion of unmodified albumin, and unaltered micropinocytic ingestion of native ferritin. These results indicate that nonenzymatic glycosylation of serum albumin may result in rapid vesicle-mediated extravasation of albumin. Chronic microvascular leakage of glycosylated albumin could contribute to the pathogenesis of diabetic microangiopathy.
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43
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Yamazaki A, Sen I, Bitensky MW, Casnellie JE, Greengard P. Cyclic GMP-specific, high affinity, noncatalytic binding sites on light-activated phosphodiesterase. J Biol Chem 1980; 255:11619-24. [PMID: 6254976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Two classes of high affinity, cGMP-specific binding sites have been found in association with a peripheral membrane protein in rod outer segments. [3H]cGMP and a photoaffinity label, 8-N3-[32P]cIMP, have been used to study these cGMP binding sites. The cGMP binding sites co-migrated with rod outer segment phosphodiesterase (EC 3.1.4.17) upon Bio-Gel A-0.5m column chromatography, sucrose density gradient centrifugation, and isoelectric focusing (pI 5.35). Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the 8-N3-[32P]cIMP-labeled protein also migrated in a position identical with that of purified phosphodiesterase. Scatchard analysis, using purified phosphodiesterase, revealed the presence of two classes of cGMP binding sites with apparent KD values of 0.16 and 0.83 microM. A number of observations indicated that these high affinity, cGMP-specific binding sites are distinct from the phosphodiesterase catalytic site. cAMP, which is a substrate for phosphodiesterase, did not bind to the high affinity cGMP specific sites. Limited tryptic proteolysis of phosphodiesterase resulted in a striking activation of the catalytic activity and a 96% loss of cGMP binding. 1-Methyl-3-isobutylxanthine inhibited phosphodiesterase activity and enhanced the specific binding of cGMP. Mg2+ was necessary for phosphodiesterase activity, but not for high affinity cGMP binding. Finally, phosphodiesterase activity and the cGMP-specific high affinity sites showed different stabilities on storage in phosphate buffer. These specific high affinity cGMP binding sites may be involved in the regulation of phosphodiesterase activity.
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Shinozawa T, Bitensky MW. Co-operation of peripheral and integral membrane proteins in the light dependent activation of rod GTPase and phosphodiesterase. Photochem Photobiol 1980; 32:497-502. [PMID: 6109342 DOI: 10.1111/j.1751-1097.1980.tb03794.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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45
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Williams SK, Gillis JF, Matthews MA, Wagner RC, Bitensky MW. Isolation and characterization of brain endothelial cells: morphology and enzyme activity. J Neurochem 1980; 35:374-81. [PMID: 6108994 DOI: 10.1111/j.1471-4159.1980.tb06274.x] [Citation(s) in RCA: 114] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Microvessels were isolated from rat brain using a double collagenase treatment which removed the endothelial basement membranes. The isolate was characterized by intact luminal and abluminal membranes and an absence of pericytes and astrocyte membranes. Minimal contamination by 5'-nucleotidase, an enzyme believed exclusively localized within the plasma membranes of neuroglia, established the purity of the isolated microvessels. Enrichment of alkaline phosphatase and gamma-glutamyl transpeptidase activity in microvessel preparations supports the endothelial localization of these enzymes.
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46
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Rasenick MM, Bitensky MW. Partial purification and characterization of a macromolecule which enhances fluoride activation of adenylate cyclase. Proc Natl Acad Sci U S A 1980; 77:4628-32. [PMID: 6933510 PMCID: PMC349898 DOI: 10.1073/pnas.77.8.4628] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Fluoride activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] is significantly enhanced (2 to 5 times) by a protein factor isolated from rat brain. The fluoride-dependent adenylate cyclase stimulator (FCS) is nondialyzable, trypsin-labile, and stable at 90 degrees C for 10 min. FCS stimulates adenylate cyclase activity only in the presence of NaF (2-25 mM) and this effect is independent of added GTP, 5'-guanylylimidodiphosphate, or calcium. FCS has been purified roughly 3000-fold from a 12,000 X g supernatant fraction of rat brain homogenate. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis and sucrose density gradient sedimentation suggest that FCS is a monomer with an apparent Mr of 59,000. Isoelectric focusing indicates FCS has a pI of 8.9. FCS from rat brain stimulates fluoride-activated adenylate cyclase from a variety of cell types, and FCS can also be isolated from rat liver. The effects of FCS are not reversed by washing membranes when the membranes and FCS are preincubated with NaF. The Km of adenylate cyclase for ATP and the fluoride concentration causing half-maximal activation are unchanged by FCS; however, FCS increases the Vmax by 2.5-fold. FCS may act to increase the catalytic efficiency of fluoride-activated complexes of the GTP-binding unit with adenylate cyclase or to enhance the formation of additional active complexes.
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47
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Block LH, Aloni B, Biemesderfer D, Kashgarian M, Bitensky MW. Macrophage migration inhibition factor: interactions with calcium, magnesium, and cyclic AMP. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 1978; 121:1416-21. [PMID: 212481] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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48
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49
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Wheeler GL, Bitensky MW. A light-activated GTPase in vertebrate photoreceptors: regulation of light-activated cyclic GMP phosphodiesterase. Proc Natl Acad Sci U S A 1977; 74:4238-42. [PMID: 200909 PMCID: PMC431914 DOI: 10.1073/pnas.74.10.4238] [Citation(s) in RCA: 161] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
We have been studying the mechanism by which light and nucleoside triphosphates activate the discmembrane phosphodiesterase (oligonucleate 5'-nucleotidohydrolase; EC 3.1.4.1) in frog rod outer segments. GTP is orders of magnitude more effective than ATP as a cofactor in the light-dependent activation step. GTP and the analogue guanylyl-imidodiphosphate function equally as allosteric activators of photoreceptor phosphodiesterase rather than participating in the formation of a phosphorylated activator. Moreover, we have found a light-activated (5-fold) GTPase which participates in the modulation of photoreceptor phosphodiesterase. This GTPase activity appears necessary for the reversal of phosphodiesterase activation in vitro and may play a critical role in the in vivo regulation of light-sensitive phosphodiesterase. The K(m) for GTP in the light-activated GTPase reaction is <1 muM. The light sensitivity of this GTPase (number of photons required for half-maximal activation) is identical to that of light-activated phosphodiesterase. The GTPase action spectrum corresponds to the absorption spectrum of rhodopsin. There is, in addition, a light-insensitive GTPase activity with a K(m) for GTP of 90 muM. At GTP concentrations above 5 muM, there is no appreciable activation of GTPase activity by light. The substrate K(m) values for guanylate cyclase, light-activated GTPase, and light-activated phosphodiesterase order an enzyme array that might permit light to simultaneously cause the hydrolysis of both the substrate and product of guanylate cyclase. These findings reveal yet another facet of light regulation of photoreceptor/cyclic GMP levels and also provide a striking analogy to the GTP regulation of nonphotoreceptor, hormone-sensitive adenylate cyclase.
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Matuo Y, Wheeler MA, Bitensky MW. Small fragments from the A subunit of cholera toxin capable of activating adenylate cyclase. Proc Natl Acad Sci U S A 1976; 73:2654-8. [PMID: 60760 PMCID: PMC430706 DOI: 10.1073/pnas.73.8.2654] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Exposure of cholera toxin to membrane particles prepared from sarcoma 180 cells gives rise to a variety of fragments which are capable of activating adenylate cyclase [ATP:pyrophosphate-lyase (cyclizing), EC 4.6.1.1]. A major component of these fragments has an apparent molecular weight in the 8,000-10,000 range. The smallest stimulatory fragment has a molecular weight of approximately 1400. The small size of the fragments is confirmed by Sephadex gel filtration, in the presence of either sodium dodecyl sulfate or formic acid. These fragments are produced from holotoxin or its A subunit by protease(s) found in sarcoma membrane particles. Production of fragments appears optimal in 40-60 min at 30 degrees and pH 7, and is prevented by protease inhibitors. The ability of the small fragments to activate adenylate cyclase is reversed by anti-holotoxin, but not anticholeragenoid, antibodies. These fragments require NAD for the activation of adenylate cyclase and are fully active after heating at 90 degrees for 5 min (pH 7).
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