δ‐l‐(α‐Aminoadipoyl)‐l‐cysteinyl‐d‐valine synthetase: isolation of l‐cysteinyl‐d‐valine, a ‘shunt’ product, and implications for the order of peptide bond formation

摘要

> class="smallCaps">l-Cysteinyl- class="smallCaps">d-valine was isolated from incubations of class="smallCaps">l-glutamate, class="smallCaps">l-cysteine and class="smallCaps">l-valine with δ- class="smallCaps">l-(α-aminoadipoyl)- class="smallCaps">l-cysteinyl- class="smallCaps">d-valine synthetase and identified by 1H NMR and electrospray ionization MS. This is entirely consistent with our prior proposal (Shiau, C.-Y., Baldwin, J.E., Byford, M.F., Sobey, W.J. and Schofield, C.J. (1995) FEBS Lett. 358, 97–100) that the α-peptide bond between cysteine and valine is formed before the δ-peptide bond between α-aminoadipate and cysteine. The inclusion of class="smallCaps">l-glutamate, an analogue of class="smallCaps">l-α-aminoadipate, did not result in a detectable amount of tripeptide product, but did increase apparent yields of class="smallCaps">l-cysteinyl- class="smallCaps">d-valine. Conceivably, formation of the class="smallCaps">l-glutamyladenylate stimulates synthesis of the cysteinyl-valine dipeptide indirectly via a conformational change in the enzyme.