Incubation of [2-2H]-valine with purified ACV synthetase from both Cephalosporium acremonium and Streptomyces clavuligerus produced L-δ-(α-aminoadipoyl)-L-cysteinyl-D-valine (ACV), determined by the essentially complete (>95%) loss of deuterium from the α position of the incorporated valine. Incubations with deuterium oxide/water as solvent produced ACV with significant incorporation of deuterium into the valinyl residue. These observations confirm the prior proposal that a single multifunctional enzyme is responsible for both the formation of the peptide bonds of ACV and the epimerisation of the valinyl residue.
