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A Pfohl-Leszkowicz S Galiegue-Zouitina B Bailleul M H Loucheux-Lefebvre G Dirheimer 《FEBS letters》1983,163(1):85-88
Both the initial velocity and the overall methylation of Ac-4HAQO modified DNA by a calf brain DNA (cytosine-5-)-methyltransferase are increased as compared to native DNA. The affinity of the modified DNA for the enzyme decreases as a function of the extent of the modification. Heat-denatured, single-stranded DNA shows exactly the opposite results: the more it is modified, the less it is methylated. The poly(dG-dC) X poly(dG-dC) modified by 4NQO is as well methylated as the non-modified one. The carcinogen may induce a tertiary structure favouring the 'walking' of the enzyme along the DNA. The hypermethylation caused by this carcinogen could have a significance in gene activity and cellular differentiation. 相似文献
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The secondary structures of cow and sheep kappa-caseins were established according to the predictive rules of Chou and Fasman. The diagrams derived from this treatment allowed us to study the chymosin sensitive bond (milk-clotting process), as well as the glycosylation and phosphorylation sites, found to be situated in beta-turns. Despite a high variability between the primary structures of the COOH-terminal part (caseinoglycopeptide) of cow, sheep, and also other caseins, the secondary structures of the biologically important sites were found to be conserved. 相似文献
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H. Kozlowski J. P. Aubert M. Gusse P. Chevaillier M. H. Loucheux-Lefebvre 《Biopolymers》1984,23(7):1241-1248
The interaction of Cu(II) with the protamine scylliorhinine Z3 was studied by means of CD measurements. At a 1:1 molar ratio, three complexes are formed. (1) In the pH range 5–6.5, the results suggest the formation of a five-membered chelate ring through the coordination of two nitrogen atoms, the N-terminal and the contiguous peptide nitrogen. (2) At pH ≥ 6.4, there is involvement of the lateral NH2 group of Arg; at pH 6.5–8, the formation of a 3N cupric complex is strongly suggested. (3) At pH ≥ 8, results indicate the formation of a 4N complex as a major species in Cu(II)-Z3 solution. The transformation from a 2N to a 3N complex, and from a 3N to a 4N complex was followed with the help of the σ(αNH2) → Cu(II) charge-transfer dichroic band transitions. At Cu(II):Z3 molar ratios ≥ 2 and at pH > 8, a new dichroic band appears, indicating the involvement of the tyrosine residue side chain in metal-ion complexation. 相似文献
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Guanyl-C8-arylamination of DNA by the ultimate carcinogen of 4-nitroquinoline-1-oxide: a spectrophotometric titration 总被引:3,自引:0,他引:3
Native and denatured DNAs and polynucleotides were modified by 4-acetoxyaminoquinoline-1-oxide, the ultimate carcinogen of 4-nitroquinoline-1-oxide (4 NQO). The N-( deoxyguanosin -C8-yl)-4-aminoquinoline-1-oxide adduct, the so-called "dG III," was quantified on the DNA and on poly(dG-dC) in absorption spectroscopy, by using a spectral property of dG III, i.e., the variation of the absorption spectrum as a function of the pH. Using the "free-dG III" absorption reference spectra, a simple graphic determination of the percentage of dG III was established by recording the absorption spectra of the 4-acetoxyaminoquinoline-1-oxide-modified polymers. It was found that the dG III adduct accounts for about 30% of the total modification in the case of native modified DNA and poly(dG-dC) and for about 70% in the case of denatured modified DNA. 相似文献
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Jean-Pierre Aubert Gérard Biserte Marie-H. Loucheux-Lefebvre 《Archives of biochemistry and biophysics》1976,175(1):410-418
The secondary structure of the peptide segment around the carbohydrate-peptide linkage in glycoproteins was predicted by using the Chou and Fasman determination. Such a study was carried out for 9 O-glycosidically linkages and 28 N-glycosidically linkages. In the case of O-glycosidically linkages, the residue Ser or Thr involved in the linkage always belongs to a β-turn. In the case of N-glycosidically linkages, 19 out of the 28 Asn studied belong to a β-turn. A predicted determination concerning the whole protein moiety of 9 glycoproteins in order to obtain some information concerning the spatial organization of the entire glycoprotein was carried out also. It seems that carbohydrate moiety takes place outside the glycoprotein. 相似文献
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Critical steps in the disassembly and reassembly of neurofilaments, the intermediate filaments of neurons, have been investigated. Bovine neurofilament subunits (Mr 210 000, 160 000 and 70 000) were purified by urea-polyacrylamide gel electrophoresis and renatured by dialysis against several non-denaturing buffers. The quality of the protein renaturation was measured by circular dichroism. The spectra of renatured neurofilament subunits were interpreted in terms of secondary structure and this showed that the solubilization of proteins in guanidine-HCl buffers is more suitable than in urea buffer for a good recovery of a filamentous structure. Furthermore, it is shown that (i) the three neurofilament subunits exhibit specific CD spectra, with shapes reminiscent of those obtained for the alpha/beta class of proteins and that (ii) there is good correlation between CD spectra, the state of renaturation and the ability of the proteins to assemble into filamentous structures. We conclude that CD studies of neurofilament proteins should help in understanding the numerous variables affecting the disassembly and reassembly of neurofilaments. 相似文献
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J.P. Aubert N. Helbecque M.H. Loucheux-Lefebvre 《Archives of biochemistry and biophysics》1981,208(1):20-29
Many proteins are glycosylated and widely distributed. Knowledge of the biosynthetic pathway is of great interest in elucidating the exact role of the oligosaccharide chain of the glycoproteins. It is now possible to glycosylate carbohydrate-depleted or chemically denatured glycoproteins or synthetic Asn-X-Thr/Ser-containing peptides in a cell-free system. The results obtained showed that it is possible to glycosylate a tripeptide but that the yield (of glycosylation) increases as the length of the peptide increases. We have shown that in native glycoproteins, the oligosaccharide chains are always situated in a β-turn. It seemed so very interesting to see if this condition was necessary for the glycosylation. To elucidate this problem, synthetic peptides were tested as glycosyl acceptors using hen oviduct membranes as enzyme source. These peptides were studied by circular dichroism in aqueous lipid mixtures and the results showed that the presence of a secondary structure in the lipid state promotes greatly the yield of glycosylation. 相似文献