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

Abstract

Propargylglycine (2-amino-4-pentynoate) and vinylglycine (2-amino-3-butenoate) were examined as substrates and possible inactivators of 2 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 acitve site residue rather than the FAD coenzyme and occurs once every 2000 turnovers. The recent observation of Horiike etal that D-propargylglycine is oxidized with a time-dependent loss of activity of D-amino acid oxidase was confirmed and mechanistic aspects of this inactivation were examined. The extent of residual oxidase activity, insensitive to further inactivation, is about 2%, at which point 1.7 labels/subunit have been introduced with propargyl[2-14C]glycine as substrate. L-Propargylglycine is a substrate but not an inactivator of L-amino acid oxidase and the product that accumulates in the nonnucleophilic N-2-hydroxyethylpiperazine-N''-2-ethanesulfonic acid buffer is acetopyruvate. In the presence of butylamine-HCl, a species with .lambda.max 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 propargylglycine show inactivation specificity, then, for L- and D-amino acid oxidase, respectively.