title: Valyl-tRNA synthetase from chick embryo brain. Properties of the sulfhydryl groups.
abstract: The number of thiol groups in valyl-tRNA synthetase [L-valine tRNA ligase (AMP) E.C.6.1.1.9] isolated from chick embryo brain was determined. Titration with 5.5'-dithiobis(2-nitrobenzoic) acid showed 11 free SH groups calculated on the basis of a molecular weight of 110000 daltons. In 8M urea reaction with DTNB revealed 1 additional SH-group. Binding of substrates to the active site of the molecule decreased the number of titratable SH-groups. The modification of enzyme activity was studied by the use of thiol reagents: metal ions Ag+, Cu2+, Hg2+ and pCMB. The ATP-PPi exchange activity of valyl-tRNA synthetase was significantly less inhibited by metal ions than the aminoacylation activity. SH-groups essential for tRNA acylation were not required for the activation of valine. After gamma irradiation of valyl-tRNA synthetase the number of SH-groups diminished parallel with the decrease in enzyme activity.
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002642:Chick Embryo; D002729:Chloromercuribenzoates / Q000494:pharmacology; D003300:Copper / Q000494:pharmacology; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D007700:Kinetics; D008628:Mercury / Q000494:pharmacology; D008970:Molecular Weight; D012834:Silver / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000032:analysis; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D014637:Valine-tRNA Ligase / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D002729:Chloromercuribenzoates; D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D012834:Silver; D003300:Copper; D004228:Dithionitrobenzoic Acid; D000604:Amino Acyl-tRNA Synthetases; D014637:Valine-tRNA Ligase; D008628:Mercury