L-vinylglycine is an alternative substrate as well as a mechanism-based inhibitor of 1-aminocyclopropane-1-carboxylate synthase

L-Vinylglycine (L-VG) has been shown to be a mechanism-based inhibitor of 1 -aminocyclopropane-1-carboxylate (ACC) synthase [Satoh, S., and Yang, S. F. (1989) Plant Physiol. 91, 1036-1039] as well as of other pyridoxal phospha te-dependent enzymes. This report demonstrates that L-VC is primarily an al ternative substrate for the enzyme. The L-VG deaminase activity of ACC synt hase yields the products alpha-ketobutyrate and ammonia with a k(cat) value of 1.8 s(-1) and a K-m value of 1.4 mM. The k(cat)/K-m of 1300 M-1 s(-1) i s 0.17% that of the diffusion-controlled reaction with the preferred substr ate, S-adenosyl-L-methionine. The enzyme-L-VG complex partitions to product s 500 times for every inactivation event. The catalytic mechanism proceeds through a spectrophotometrically detected quinonoid with lambda(max) of 530 nm, which must rearrange to a 2-aminocrotonate aldimine to yield final pro ducts. Alternative mechanisms for the inactivation reaction are presented, and the observed kinetics for the full reaction course are satisfactorily m odeled by kinetic simulation. The inactive enzyme is an aldimine with lambd a(max) of 432 nm. It is resistant to NaBH3CN but is reduced by NaBH4. ACC s ynthase is now expressed in Pichia pastoris with an improved yield of 10 mg /L.