The heterogeneity of cytoplasmic deoxyribonucleic acid polymerase from Physarum polycephalum

Abstract

Cytoplasmic DNA polymerase (DNA deoxynucleotidyltransferase, EC 2.7.7.7) was partially purified from Physarum polycephalum. The first step of the purification procedure utilized the fact that the enzyme on gel filtration behaves in anomalous fashion. The second step was either ion-exchange chromatography or sucrose-density-gradient centrifugation. The partially purified DNA polymerase was heterogeneous and at least four species with different sedimentation coefficients (5.5S, 7.2S, 8.6S and 11.5S) were detected. Calculated molecular weights indicated a tendency for stoicheiometric polypeptide aggregation, accompanied by an alteration of the three-dimensional structure froma compact spheroid to a more open elliptical form. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and computed molecular weights suggest an active protomer in the range of 113000 daltons; all data pertain to I 0.045, which was maintained during the whole procedure.