Synthesis of 3-N-ribosyluric acid 5'-monophosphate by red cells of the bovine fetus.

Although 3-N-ribosyluric acid (3-RUA) was not detected in the red cells of bovine fetuses, 3-N-ribosyluric acid 5'-monophosphate, the immediate precursor of 3-RUA, was synthesized from uric acid and 5-phosphoribosyl-1-pyrophosphate (PRPP) by hemolysates of fetal red cells. These preparations also synthesized 3-N-ribosylxanthine 5'-monophosphate from xanthine and PRPP. Partially purified extracts of fetal and adult erythrocytes of cattle had similar enzyme activity and the same specificity toward xanthine and orotic acid. Therefore, it was concluded that the absence of 3-RUA in fetal red cells was not a result of lack of the enzyme orotate phosphoribosyltransferase (EC 2.4.2.10).