Thymidine Kinase Enzyme Variants in Physarum polycephalum in Vitro Interconversion of the Enzyme Variants1

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Abstract
Isoelectric focusing of plasmodial extracts of Physarum polycephalum demonstrated the presence of several multiple enzyme variants of thymidine kinase, which appear sequentially during the nuclear division cycle. Variants (A)+(A1) are the only enzyme variants found in the late G2-phase, whereas the variants (C)+(C1) are only present at the time of mitosis and S-phase (1, 2). Evidence is presented that multiple forms of thymidine kinase (A)+(A1) with high pI arise by dephosphorylation of a primary translation product with low pI (C and/or C1). The thymidine kinase fractions (A)+(A1) and (C)+(C1) were separated and partially purified by DEAE-cellulose chromatography. The enzyme variants (C)+(C1) are converted in vitro by an endogenous enzymatic factor as well as by bacterial alkaline phosphatase into the variants (A)+(A1).