SUBSTRATE-SPECIFICITY OF L-DELTA-(ALPHA-AMINOADIPOYL)-L-CYSTEINYL-D-VALINE SYNTHETASE FROM CEPHALOSPORIUM-ACREMONIUM - DEMONSTRATION OF THE STRUCTURE OF SEVERAL UNNATURAL TRIPEPTIDE PRODUCTS

Potential substrates for L-delta-(alpha-aminoadipoyl)-L-(cysteinyl)-D-valine (ACV) synthetase were initially identified using both the amino-acid-dependent ATP reversible arrow pyrophosphate exchange reaction catalysed by the enzyme and the incorporation of C-14-radiolabelled cysteine and valine into potential peptide products. S-Carboxymethylcysteine was an effective substitute for alpha-aminoadipate and both allylglycine and vinylglycine could a substitute for cysteine, indicating that the thiol group of cysteine is not essential for peptide formation. L-allo-Isoleucine but not L-isoleucine substituted effectively for valine. The structures of the presumed peptide products derived from these amino acids were confirmed by combined use of electrospray-ionization m.s. (e.s.m.s.) and H-1 n.m.r. These results clearly indicate that, in common with other peptide synthetases, but in contrast with ribosomal peptide synthesis, ACV synthetase has a relatively broad substrate specificity.