Studies on the Mechanism and Stereospecificity of the Urocanase Reaction.

1. Nuclear-magnetic-resonance spectroscopy was used to follow the course of the urocanase reaction. It was shown that 3-(4'-hydroxyimidazol-5'-yl)-propionate is the true enzyme product and that it spontaneously tautomerises to racemic 3-(imidazol-4'-one-5'-yl)-propionate. 2. Conversion of urocanate in deuterium oxide by a crude-enzyme preparation from Pseudomonas putida led to a product containing two adjacent CH²H-groups. Oxidative degradation of this product afforded optically pure (RR)-[²H2]succinic acid. This fining defines the stereochemistry of proton addition to the double bond of urocanate. [ABSTRACT FROM AUTHOR]