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Direct determination of creatine kinase equilibrium constants with creatine or cyclocreatine substrate 总被引:1,自引:0,他引:1
The equilibrium constants of two reactions catalyzed by rabbit muscle creatine kinase with creatine or cyclocreatine as substrate were determined by 31P-NMR. The value of the equilibrium constant with creatine as substrate was 172.10(7) M(-1) in agreement with previous work (Veech, R.L., Lawson, J.W.R., Cornell, W. and Krebs, H.A. (1979) J. Biol. Chem 254, 6538-6547). The value with cyclocreatine was 5.62.10(7) M(-1) and the ratio of the two constants is 30.6. It was possible to determine the ratio of the two equilibrium constants in a reaction mixture containing both substrates since it was found that the 31P resonances of P-creatine and P-cyclocreatine were well resolved. The ratio of K1/K2 determined in such experiments was 34.6, of the same order as previously reported by Annesley and Walker (Annesley, T.M. and Walker, J.B. (1977) Biochem. Biophys. Res. Commun. 74, 185-190). 相似文献
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C L Cohn J R Sprinkle J Alam M Hermodson T Meyer D W Krogmann 《Archives of biochemistry and biophysics》1989,270(1):227-235
The low-potential cytochrome c550 has been purified from the cyanobacterium Microcystis aeruginosa and its amino acid sequence has been determined. The protein contains 135 amino acid residues with the Cys-X-X-Cys-His heme binding site at residues 37 to 41. The sequence from residue 28 to 45 shows similarity to cytochrome c553 residues 1 to 18 when the heme binding sites are aligned. Another region of similarity is in the carboxyl-terminal regions of these two proteins. The two aligning regions of cytochrome c553 correspond to helical segments in other related cytochromes. A partial sequence of cytochrome c550 from Aphanizomenon flos-aquae was obtained and showed a 48% identity to the sequence of the M. aeruginosa cytochrome. The single methionine residue in cytochrome c550 of M. aeruginosa occurs at position 119 but there is no methionine in this region in the A. flos-aquae cytochrome, indicating that methionine is not the sixth ligand to the heme iron atom. Histidine 92 is a possible sixth ligand in M. aeruginosa cytochrome c550. The far-uv circular dichroism spectrum indicates that this protein is approximately 17% alpha helix, 42% beta-pleated sheet, and 41% random coil. 相似文献
6.
J A Cohn N C Dougherty W F King 《Biochemical and biophysical research communications》1989,165(2):810-816
Protein phosphorylation responses in intact enterocytes were examined by stimulating 32Pi-labeled T84 cell monolayers with histamine and resolving proteins by two-dimensional gel electrophoresis. Histamine increases 32P-incorporation into two acidic proteins of Mr 83,000 and of Mr 29,000, designated p83 and p29. Labeling of p83 and p29 is also increased in cells exposed to ionomycin, but not in cells exposed to vasoactive intestinal peptide under conditions resulting in cAMP-mediated secretion and cAMP-stimulated protein phosphorylation. When T84 cell fractions are incubated with [gamma-32P]ATP, labeling of p83 is stimulated by Ca++, but not by cAMP. Thus, histamine stimulates Ca++-mediated protein phosphorylation during the regulation of Cl- secretion. 相似文献
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D Emilie C Wallon P Galanaud A Fischer D Olive J F Delfraissy 《Journal of immunology (Baltimore, Md. : 1950)》1988,141(6):1912-1918
We examined the role of the lymphocyte function-associated (LFA)3 molecule in human B cell response. A mAb to this molecule did not influence B cell proliferation induced by anti-mu antibody and IL. In contrast, the same mAb inhibited the specific T-dependent B cell response induced by a particulate Ag. In the same line, two anti-CD2 mAb (directed toward the T11-1 and T11-2 epitopes) inhibited this response, whether used alone or in association. These inhibitions took place at an early stage of the response, and anti-LFA3 and anti-CD2 mAb acted on B cells and T cells, respectively. In contrast, when T cell help was provided by exogenous IL-2, the B cell response was resistant to the inhibitory effect of anti-LFA3 mAb. Taken together, these results indicate that the LFA3-CD2 pair play a major role in the direct T-B interaction required for T cell help. 相似文献
8.
Osteogenesis imperfecta due to recurrent point mutations at CpG dinucleotides in the COL1A1 gene of type I collagen 总被引:7,自引:3,他引:4
Charles J. Pruchno Daniel H. Cohn Gillian A. Wallis Marcia C. Willing Barbra J. Starman Xiaoming Zhang Peter H. Byers 《Human genetics》1991,87(1):33-40
Summary Most individuals with osteogenesis imperfecta (OI) are heterozygous for dominant mutations in one of the genes that encode the chains of type I collagen. Each of the more than 30 mutations characterized to date has been unique to the affected member (s) of the family. We have determined that two individuals with a progressive deforming variety of OI, OI type III, have the same new dominant mutation [1(I)gly154 to arg] and that two unrelated infants with perinatal lethal OI, OI type II, share a second new dominant muation [1(I)gly1003 to ser]. These mutations occurred at CpG dinucleotides, in a manner consistent with deamination of a methylated cytosine residue, and raise the possibility that CpG dinucleotides are common sites of recurrent mutations in collagen genes. Further, these findings confirm that the OI type-III phenotype, previously thought to be inherited in an autosomal recessive manner, can result from new dominant mutations in the COL1A1 gene of type-I collagen. 相似文献
9.
In vivo or in vitro selection for resistance to natural cytotoxic cell lysis selects for variants with increased tumorigenicity 总被引:1,自引:0,他引:1
P Q Patek Y Lin J L Collins M Cohn 《Journal of immunology (Baltimore, Md. : 1950)》1986,136(2):741-745
Experiments were designed to test the hypothesis that transformed cells that are NC sensitive must escape NC activity if they are to grow as tumors in normal individuals. NC-resistant variants were selected either in vivo or in vitro from NC-sensitive cell lines that grow as tumors in immunodeficient mice but not in syngeneic normal mice. The tumorigenicity of cloned NC-resistant variants was compared with the parental cell lines and to cell lines that went through the selection procedure, but after cloning remained NC sensitive. Cloned NC-resistant cell lines derived from tumors that developed in x-irradiated nude mice after the injection of an NC-sensitive cell line are tumorigenic in normal mice, whereas cloned NC-sensitive cell lines derived from the same tumors are unable to grow as tumors in normal mice. Similarly, six of seven NC-resistant cloned cell lines independently isolated after in vitro selection for NC-resistance are tumorigenic in normal mice, whereas cloned NC-sensitive cell lines isolated from the same in vitro selected populations are not tumorigenic in normal mice. Thus, either the in vivo or in vitro selection of NC-resistant cells selects for cells tumorigenic in normal mice; these findings, along with our previous observations that selection for cells tumorigenic in normal mice selects for NC resistance, provide compelling evidence that escape from NC activity is required before some transformed cells can grow as tumors in normal mice. 相似文献
10.
The contribution deals with the phytocenological analysis of theRondeletio correifoliae-Andropogonetum multinervosi, an endemic savanna association occuring on the Siguanea Hills (Sierra de la Siguanea) near the Colony Hotel. 相似文献