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Pyrimidine Synthesis Pathway Enzymes and Orotic Acid in Bovine Mammary Tissue

Department of Dairy Science, University of Illinois, Urbana 61801

ABSTRACT

Studies were initiated to determine if the high orotic acid in bovine (ruminant) milk is indicative of a pathway of pyrimidine synthesis different from that in other bacterial and mammalian systems where this metabolic intermediate is normally low. Elevated orotic acid was not found in a variety of other body fluids or tissues of the bovine which included the apparent intracellular level in the tissue itself when corrected for its milk content. Analyses for three enzymes on the pathway of pyrimidine synthesis (dihydroorotic acid dehydrogenase, orotidine 5'-phosphate pyrophosphorylase, and orotidine 5'-phosphate decarboxylase) indicated adequate activity, thus, contrasting with other situations of orotic acid accumulation where activity of some of these enzymes is lacking. The results suggest that the normal pathway for pyrimidine synthesis is operational in bovine mammary tissue and that orotic acid accumulation must be explained by an unknown altered functioning of this pathway possibly related to the milk secretion process.