Pyrimidine Synthesis Pathway Enzymes and Orotic Acid in Bovine Mammary Tissue

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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 nor- really 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 path- way of pyrimidine synthesis (dihydro- orotic acid dehydrogenase, orotidine 5"- phosphate pyrophosphorylase~ and oroti- dine 5"-phosphate decarboxylase) indicated adequate activity, thus, contrasting with other situations of orotic acid accumula- tion where activity of some of these en- zymes is lacking. The results suggest that the normal pathway for pyrimidine syn- thesis is operational in bovine mammary tissue and that orotic acid accumulation must be explained by an unknown altered functioning of this pathway possibly re- lated to the milk secretion process.