Subcellular localization of pyrimidine synthesis enzymes in bovine mammary tissue

Subcellular localization of enzymes of the pyrimidine biosynthetic pathway was determined in lactating bovine mammary tissue. Aspartate transcarbamylase was associated with a membrane portion of the microsomal cell fraction. Dihydroorotate dehydrogenase w3as in the mitochondrial fraction with no evidence for a cytosolic enzyme requiring pyridine nucleotides. Orotate phosphoribosyltransferase was in the cytosol of the cell. The significance of these findings to other mammalian cells and orotic acid accumulation in bovine milk is discussed.