Vinylglycine and proparglyglycine: complementary suicide substrates for L-amino acid oxidase and D-amino acid oxidase.

Abstract

Proparglyglycine (2-amino-4-pentynoate) and vinylglycine (2-amino-3-butenoate) have been examined as substrates and possible inactivators of two flavo enzymes, D-amino acid oxidase from pig kidney and L-amino acid oxidase from Crotalus adamanteus venom. Vinylglycine is rapidly oxidized by both enzymes but only L-amino acid oxidase is inactivated under assay conditions. The loss of activity probably involves covalent modification of an active site residue rather than the flavin adenine dinucleotide coenzyme and occurs once every 20000 turnovers. We have confirmed the recent observation (Horiike, K, Hishina, Y., Miyake, Y., and Yamano, T. (1975) J, Biochem. (Tokyo), 78, 57) that D-proparglglycine is oxidized with a time-dependent loss of activity by D-amino acid oxidase and have examined some mechanistic aspects of this inactivation, The extent of residual oxidase activity, insensitive to further inactivation, is about 2%, at which point 1.7 labels/subunit have been introduced with propargly[2-14C]glycine as substrate. L-Proparglyclycine is a substrate but not an inactivator of L-amino acid oxidase and the product ahat accumulats in the nonnucleophilic N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer is acetopyruvate. In the presence of butylamine HCl, a species with lambdaman 317 nm (epsilon = 15 000) accumulates that may be a conjugated eneamine adduct. The same species accumulates from D-amino acid oxidase oxidation of D-propargylglycine prior to inactivation; the inactivated apo D-amino acid oxidase has a new peak at 317 nm that is probably a similar eneamine. A likely inactivating species is 2-keto-3,4-pentadienoate arising from facile rearrangement of the expected initial product 2-keto 4 pentynoate. Vinylglycine and proparglyglycine show inactivation specificity, then, for L-and D-amino acid oxidase, respectively.