Erythrocyte UMP Synthetase Activity

Abstract

Orotate phosphoribosyltransferase (OPRT) and OMP decarboxylase (ODC), the last two enzymes in the de novo synthesis of pyrimidine nucleotides, reside in two separate domains of a single polypeptide chain, forming the so called UMP synthetase (UMPs).¹ UMPs is responsible for the conversion of orotic acid to UMP, which in turn can be converted into the other pyrimidine nucleotides. One or both activities are known to be defective in human mutants with hereditary oroticaciduria, a rare disorder presenting with megaloblastic anemia, mental retardation and diverse additional features.¹ Diagnosis can be effected by measuring OPRT and ODC activities in the erythrocytes, which normally metabolise extracellular orotate through this salvage pathway, though lacking the de novo pyridine synthesis.