IDENTIFICATION OF RBOXY-1-(1H-IMIDAZOL-4-YL)ETHYL]-3-MERCAPTOPYRUVIC ACID WITH A METABOLIC INTERMEDIATE BETWEEN S-[2-CARBOXY-1-(1H-IMIDAZOL-4-YL)ETHYL]-L-CYSTEINE AND ARBOXY-1-(1H-IMIDAZOL-4-YL)ETHYL]-3-MERCAPTOLACTIC ACID

rboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptopyruvic acid (I) was chemic ally synthesized in 15% yield by incubating a reaction mixture of tran s-urocanic acid and 3-fold excess of 3-mercaptopyruvic acid at 45 degr ees C for 6 days. The synthesized compound was characterized by fast-a tom-bombardment mass spectrometry and high-voltage paper electrophores is. Compound I was identified with a product of an enzymatic reaction of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteine (II) with rat li ver homogenate in a phosphate buffer, pH 7.4. Compound I was degraded to arboxy-1-(1H-imidazol-4-yl)ethyl]-3-mercaptolactic acid (III), a co mpound previously found in human urine [Kinuta et al. (1994) Biochem J 297: 475-478], by incubation with rat liver homogenate. From these re sults, we suggest that compound I is a metabolic intermediate for the formation of compound III from compound II. The present pathway follow s a formation of compound II from -[2-carboxy-1-(1H-imidazol-4-yl)ethy l]gluthathione [Kinuta et al. (1993) Biochim Biophys Acta 1157: 192-19 8], a proposed metabolite of L-histidine.