Characterization of the purified cytosolic thymidine kinase from murine ehrlich ascites tumor: interconversion of two different relative molecular weight forms.

Cytosolic thymidine kinase was purified 18,000-fold of the homogenate from murine Ehrlich ascites tumor, using the [p-aminophenyl 3' -dTMP]-CH-Sepharose affinity column. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme showed a single protein band of molecular weight 26,000. Two different forms, relative molecular weight 50,000 and 70,000, were found by gel filtration, depending on the existence of dithiothreitol, ATP and other nucleotides. These agents also stabilize and stimulate the enzyme activity. The existence of two forms was also manifested by DEAE-Sephacel column chromatography, where the 50,000 form was eluted by 50 mM NaCl and the 70,000 form by 400 mM NaCl.