Purification and Kinetic Properties of Brain Orotidine 5′-Phosphate Decarboxylase

Abstract

Abstract Orotidine 5'-phosphate decarboxylase has been purified approximately 600-fold from cow brain. The purified enzyme catalyzes the irreversible decarboxylation of orotidine 5'-phosphate to form uridine 5'-phosphate and is inhibited by cytidine monophosphate g uridine monophosphate g cytidine diphosphate g uridine diphosphate g cytidine triphosphate. From kinetic data the inhibition appears to represent a simple competitive interaction at the catalytic site. Those compounds which act as competitive inhibitors were also found to stabilize the enzyme under conditions of heat denaturation. It appears unlikely that the observed inhibition serves a role in regulating pyrimidine levels. During purification and heat denaturation experiments, activity of orotidine 5'-phosphate pyrophosphorylase appears to parallel orotidine 5'-phosphate decarboxylase activity.