The initiation of peptide formation in the biosynthesis of actinomycin.

摘要: Abstract Actinomycin Synthetase II (ACMS II), which activates threonine and valine by a thioltemplate mechanism during the synthesis of actinomycin half-molecule 4-methyl-3-hydroxyanthranilic acid (4-MHA) pentapeptide lactone, was purified to near homogeneity from Streptomyces chrysomallus. It is single polypeptide chain M(r) 280,000 contains 4'-phosphopantetheine as covalently bound prosthetic group. ACMS charges itself with but not 4-MHA analogue p-toluic via specific sulfhydryl group at expense ATP. Charging in thioester linkage took place, however, only when synthetase I I), 4-MHA-AMP ligase, present. In additional presence L-threonine, enzyme-bound p-toluyl-L-threonine formed on II. The latter compound also chemically synthesized adenylate added instead acid. This indicates that free intermediate reaction charging enzyme acylation are both catalyzed rather than I. Chemically thioesters coenzyme A, pantetheine, or beta-alanyl-cysteamine reacted II, threonine, ATP formation p-toluyl-threonine. contrast, p-toluyl-cysteamine inactive, structural constraints reactivity Such obviously require similarity artificial substrate enzyme's surface course reaction. Since A involved p-toluyl-threonine formation, cofactor most likely primary acceptor (or 4-MHA) initiation peptide lactone formation.