Thiol-glyoxylate adducts as substrates for rat kidney L-α-hydroxy acid oxidase

Rat kidney L-α-hydroxy acid oxidase (EC 1.1.3.15) catalyzes a rapid O₂ uptake at pH 7.5 when both glyoxylate and one of a number of various thiols are present. Thiols which are reactive in this system include: ethanethiol, 1-propanethiol, 2-mercaptoethanol, N-acetylcysteamine, propane-1,3-dithiol, dihydrolipoic acid, Coenzyme A, dephospho Coenzyme A, phosphopantetheine, and pantetheine. Notable physiological thiols that are not very reactive include: glutathione, L-cysteine and cysteamine. Presumably the substrate is a thiol-glyoxylate adduct because both the thiol and glyoxylate must be present in order to obtain a rapid enzyme-catalyzed reaction and oxalyl thioesters are the products of the enzymic reactions. Kinetic studies indicate that some of these adducts are better substrates than any others presently known. These and other results imply that a thiol-glyoxylate adduct may be the physiological substrate for L-α-hydroxy acid oxidase. A possible function for this reaction in metabolic control, mediated either by the oxalyl thioester or by oxalate, is briefly considered.