Mechanism of depsipeptide formation catalyzed by enniatin synthetase

Covalently bound intermediates of enniatin B synthesis could be isolated from enniatin synthetase by treatment with performic acid. By comparison with products of mild alkaline cleavage of authentic enniatin B they could be identified as the dipeptide D-2-hydroxyisovaleryl-N-methylvaline and the corresponding tetrapeptide. Synthesis of enniatins apparently proceeds via condensation of dipeptides. This was confirmed by the use of the substrate analogue isovaleric acid, which has shown to be a strong inhibitor for enniatin synthesis by formation of N-isovaleryl-N-methyl valine.