Preparation and characterization of S-[2-carboxy-1-1 H-imidazol-4-yl)ethyl]glutathione and its derivatives as proposed precursors of S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]cysteine, a compound found in human urine

Abstract

Formation of 3-[(carboxymethyl)thio]-3-(1 H-imidazol-4-yl)propanoic acid (I) and S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]cysteine II, compounds found in human urinee, has been demonstrated by enzymatic degradation of S-[2-carboxy-1(1 H-imidazol-4-yl)ethyl]glutathione (III). Compound (III) was chemically synthetisized in 72% yield by incubating the reaction mixture of trans-urocanic acid and 3-fold excess GSH at 65°C for 1 wk, which was accompanied by formation of N-{ S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]cysteinyl}glycine (IV) in 15% yield. S-[2-Carboxy-1-(1 H-imidazol-4-yl)ethyl]- N- γ-glutamylcysteine (V) was produced by partial hydrolysis of compound (III) in HCl. The synthesisized compounds were characterized mainly by fast-atom bombardment mass spectrometry and high-voltage paper electrophoresis as well as chemical degradation. Incubation of compound (III) with rat kidney homogenate in a Tris buffer (pH 8), formed compound (II) in 80% yield possibly via compound (IV). Yield of compound (II) was increased by adding glycylglycine to the reaction mixture. However, little degradation of compound (III) occurred in the use of rat liver, brain,heart, or spleen homogenate as the enzyme source. Compound (II) was further metabolized to compound (I) by incubation with rat kidney homogenate in a phosphate buffer of pH 7.4 From these results, we suggest that the urinary compounds are products of enzymatic degradation of compound (III) and that GSH may participate in the metabolism of urocanic acid, the first catabolite of L-histidine.