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41.
Myoglobin: cytochrome b5 interactions and the kinetic mechanism of metmyoglobin reductase 总被引:2,自引:0,他引:2
D J Livingston S J McLachlan G N La Mar W D Brown 《The Journal of biological chemistry》1985,260(29):15699-15707
Metmyoglobin (metMb) reduction by metMb reductase from heart muscle requires cytochrome b5 as electron-transfer mediator. The existence of a metMb-ferrous cytochrome b5 complex is demonstrated by mutual perturbation of the proteins' respective electrophoretic titration curves between pH 4 and 7. The same technique shows a preferential binding of cytochrome b5 over metMb by the enzyme. The paramagnetic hyperfine shifts in the cytochrome b5 1H NMR spectrum are perturbed by metMb, indicating the formation of a specific bimolecular complex with a 1:1 stoichiometry and a binding constant estimated to be less than 10 microM. The resonances assigned to the cytochrome b5 heme 6-propionate methylene group exhibit the largest complexation shifts. Computer modeling implicates lysines 47, 50, and 98 of metMb as contact points with cytochrome b5 carboxylate residues 43, 44, 60, and heme 6-propionate. The mechanism of the enzymatic reduction establishes metMb reductase as an NADH-cytochrome b5 oxidoreductase. Cytochrome b5 is reduced at near diffusion-controlled rates by the enzyme with a turnover number of 1000 min-1 X Km for the cytochrome is 0.9 microM versus 100 microM reported for the erythrocyte enzyme. Ferrous cytochrome b5 then reduces metMb nonenzymatically with an apparent rate constant of 4.9 X 10(4) M-1 min-1 X Acetylation of metMb, which does not affect its oxygen affinity or chemical reduction, renders it a poor substrate for enzymatic reduction. This study suggests a function for the three exterior lysine residues conserved in all mammalian myoglobin sequences: they are contact points for complexation with cytochrome b5. 相似文献
42.
Among the apoA-I-containing lipoproteins isolated by selected-affinity immunosorption from human serum and plasma, we have identified a subpopulation which, unlike the bulk of high density lipoproteins, has pre-beta electrophoretic mobility. This pre-beta subpopulation can be observed directly in fresh plasma by immunoelectrophoresis. It contains phospholipid and free and esterified cholesterol, but protein constitutes 90% of its mass. Apolipoprotein A-I is the predominant apolipoprotein in this subpopulation; apolipoprotein A-II and the B lipoproteins are not detected. The protein moiety of this subpopulation exhibits markedly lower helicity than that of high density lipoproteins isolated by ultracentrifugation. 相似文献
43.
G Gravante F Sorbera M Sabatino V La Grutta 《Bollettino della Società italiana di biologia sperimentale》1985,61(2):249-254
In chronic free-moving cats unilateral, low frequency, long duration stimulation of the caudate nucleus causes a significant reduction of food intake. The effects are greatest at the beginning of the stimulation. On cessation of stimulation the animals take enough food to compensate for that lost during the time of stimulation. Results are discussed either considering interrelationships between striatum and lateral hypothalamus, either regarding recent viewpoints distinguishing two striatal compartments: dorsal or "non limbic" striatal region and ventral or "limbic" striatal region. 相似文献
44.
45.
Jef D. Boeke Francois La Croute Gerald R. Fink 《Molecular & general genetics : MGG》1984,197(2):345-346
Summary Mutations at the URA3 locus of Saccharomyces cerevisiae can be obtained by a positive selection. Wild-type strains of yeast (or ura3 mutant strains containing a plasmid-borne URA3
+ gene) are unable to grow on medium containing the pyrimidine analog 5-fluoro-orotic acid, whereas ura3
– mutants grow normally. This selection, based on the loss of orotidine-5-phosphate decarboxylase activity seems applicable to a variety of eucaryotic and procaryotic cells. 相似文献
46.
47.
48.
C Di Ilio A Arduini G Del Boccio G La Rovere G Federici 《Clinical physiology and biochemistry》1986,4(2):120-124
The erythrocytes of multiple sclerosis patients with elevated superoxide dismutase levels were tested for the activities of glutathione redox cycle enzymes. No differences were observed between multiple sclerosis and normal control erythrocytes when the activities were referred to either hemoglobin concentration or lactate dehydrogenase content. Our results indicate that no adaptative changes occur in the activities of glutathione redox cycle enzymes in erythrocytes of multiple sclerosis subjects as a consequence of an elevated superoxide dismutase level. 相似文献
49.
A.S.C. Wan T.L. Ngiam S.L. Leung M.L. Go P.W.S. Heng P.N. Natarajan A. Shafiee M. Vossoghi F. Savabi C.G. Francisco R. Freire R. Hernandez J.A. Salazar E. Suarez G.A.Garcia De La Mora Y.Grillasca R. O. Jimeno 《Steroids》1983,41(3):309-320
The synthesis of esters of norethisterone (17α-ethynyl-17β-hydroxy-estr-4-en-3-one) with acids containing a benzene ring is described, two methods of esterification being compared in terms of yield and convenience. The activities of these esters as long-acting contraceptive agents have been evaluated. 相似文献
50.
A STUDY OF GLUCO-CORTICOSTEROID-INDUCED PYKNOSIS IN THE THYMUS AND LYMPH NODE OF THE ADRENALECTOMIZED RAT
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Pyknotic nuclei, observed in the thymus of steroid-treated rats, are dense, homogeneous, intensely basophilic and Feulgen positive. Under the electron microscope, the image is that of a complete segregation of the chromatin from the nuclear sap producing a margin or crescent of condensed chromatin. Approximately 30% of all small thymocytes appeared to undergo this type of degeneration within 3–4 hr after administration of the synthetic corticosteroid, dexamethasone. At this time, pyknotic thymocytes were observed in clusters, probably as a result of the activity of dense reticular cells and macrophages. Topographical and experimental data suggest the existence of a select population of steroid-sensitive thymic cells. Furthermore, on the basis of thymidine-3H incorporation studies, it appears that the steroid-sensitive population of thymocytes does not correspond to "aged" cells. In addition, many plasma cells became pyknotic after the same steroid treatment, indicating an unexpected similarity between their nuclei and those of lymphocytes. Finally, steroid failed to induce pyknosis of thymocytes in a variety of in vitro experiments, suggesting that the in vivo effect of steroid is of an indirect nature. The results are discussed in terms of (a) the nature of the nuclear changes characterizing pyknosis, (b) the hypothetical mechanism whereby steroids trigger such changes, and (c) the population of cells susceptible to steroid-induced pyknosis. 相似文献