Human erythrocytic nucleoside diphosphokinase has been found to be heterogeneous by electrofocusing, electrophoresis, and ion-exchange chromatography. Several isozymes of the nucleoside diphosphokinase seem to be present. Six distinct peaks of enzymic activity, with isoelectric points from 5.4 to 8.3, were observed both in electrofocusing and in agarese electrophoresis. The electrophoretic patterns from the pooled blood of 100 persons or from single persons of different races showed no qualitative differences. Preliminary studies with the individual electrophoretic peaks revealed molecular weights ranging from 80,000 to about 100,000 indicating that aggregation is not a factor. Marked differences in the kinetic parameters were seen: e.g., Km values for ATP were 0.083 × 10-3 and 3.0 × 10-3 M for isozymes of pI = 7.3 and 6.3, respectively. Arrhenius plots were linear for isozymes of pI = 5.4, 5.8, 6.3, and 6.8 and were biphasic for isozymes of pI = 7.3 and 8.3. Present evidence indicates that the six electrophoretic peaks are distinctly different proteins.
ASJC Scopus subject areas