Electrophoretic and kinetic studies of a new mutant red cell pyrimidine 5'-nucleotidase.

Molecular characteristics of a deficient pyrimidine 5'-nucleotidase (P5N) were studied in a partially purified red cell enzyme extract. The results showed a high Michaelis constant for uridine 5'-monophosphate, an acidic shift of the optimum pH and normal heat stability. Enzyme electrophoresis using a starch gel and histidine-citrate buffer pH 7.0 showed a single band with identical mobility to that of the 'minor' band of normal enzyme. This electrophoretic pattern supports the hypothesis that P5N deficiency is, at least in some cases, a consequence of the absence of a 'major' isoenzymatic band characteristically present in normal enzyme.