Abstract
Red blood cell (rbc) pyrimidine 5' nucleotidase deficiency (P5N) is a cytosolic enzyme system that dephosphorylates CMP, UMP, dCMP, dUMP and dTMP. The kinetics and metallosensitivities of enzyme activity were determined in normal subjects, congenital pyrimidine 5' nucleotidase deficiency (PND) and subjects with increased blood lead. The apparent Michaelis constants and Kmax suggest 3 isoenzymes of decreasing substrate affinity for 1) dUMP and dCMP, 2) dTMP, 3) UMP and CMP. In PND, activity with UMP and CMP is < 15% normal with an increased Km for both substrates. In PND rbc, enzyme activity is normal to increased with dUMP, dCMP, dTMP. These observations are consistent with the accumulation of CDP-choline and CDP-ethanolamine in PND rbc and our inability to identify, by MS or NMR, the presence of deoxypyrimidine esters in PND rbc. The maximal affinity of the enzyme for the deoxypyrimidines suggests a role in the clearance of DNA as well as RNA during red cell maturation. In vitro sensitivity to Pb2+ and Cu2+ (> 50% inhibition at 10−4) is more evident in normal rbc than PND. In rbc from lead exposed subjects, rbc P5N activity with UMP as substrate is directly correlated with the level of blood lead.
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Angle, C., Stohs, S., Cook, L. et al. 881 ERYTHROCYTE PYRIMIDINE 5′ NUCLEOTIDASE ISOENZYMES IN CONGENITAL DEFICIENCY AND IN LEAD EXPOSURE. Pediatr Res 19, 257 (1985). https://doi.org/10.1203/00006450-198504000-00911
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DOI: https://doi.org/10.1203/00006450-198504000-00911