Pyrimidine nucleotidase deficiency with active dephosphorylation of dTMP: evidence for existence of thymidine nucleotidase in human erythrocytes

Erythrocytes from a patient with classical pyrimidine nucleotidase (PyN) deficiency had less than 10% residual PyN activity with uridine 5′-monophosphate (UMP) or cytidine 5′-monophosphate (CMP) as substrate, but exhibited brisk nucleotidase activity with thymidine 5′- monophosphate (dTMP). This strongly suggests the existence of separate enzymes or isozymes of PyN in normal human erythrocytes--an hypothesis that should be tested by similar studies in other cases of severe PyN deficiency, whether induced by genetic defects or lead toxicity.