title: A comparative study of sulfhydryl groups required for the catalytic activity of gramicidin S synthetase and isoleucyl tRNA synthetase.
abstract: The sulfhydryl groups required for the catalytic activity of gramicidin S synthetase of Bacillus brevis and Escherichia coli isoleucyl tRNA synthetase were compared. In gramicidin S synthetase 2(GS 2), about four sulfhydryl groups react rapidly with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) or N-ethylmaleimide (NEM), and are essential for gramicidin S formation in the presence of gramicidin S synthetase 1 (GS 1). These sulfhydryl groups are protected against DTNB and NEM reactions by the preincubation of GS 2 with amino acid substrates in the presence of ATP and MgCl2, like the sulfhydryl groups that react rapidly with DTNB or NEM and are required for the catalytic activity of GS 1 and isoleucyl tRNA synthetase. In GS 2, GS 1, and isoleucyl tRNA synthetase, the sulfhydryl group that reacts rapidly with NEM and is required for the catalytic activity is involved in the amino acid binding as a thioester. In isoleucyl tRNA synthetase, it is suggested that isoleucine may be transferred from the isoleucine thioester enzyme complex to tRNA by a mechanism similar to that proposed for gramicidin S synthetase.
mesh_terms: D000591:Amino Acid Isomerases / Q000378:metabolism*; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001407:Bacillus / Q000201:enzymology*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology*; D005033:Ethylmaleimide / Q000494:pharmacology*; D007533:Isoleucine-tRNA Ligase / Q000378:metabolism*; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism*; D009579:Nitrobenzoates / Q000494:pharmacology*; D010453:Peptide Synthases / Q000378:metabolism*; D013438:Sulfhydryl Compounds
chemical_list: D009097:Multienzyme Complexes; D009579:Nitrobenzoates; D013438:Sulfhydryl Compounds; D004228:Dithionitrobenzoic Acid; D000591:Amino Acid Isomerases; D000604:Amino Acyl-tRNA Synthetases; D007533:Isoleucine-tRNA Ligase; D010453:Peptide Synthases; C020831:gramicidin-S-synthetase 2; D005033:Ethylmaleimide