Two Molecular Forms of Thymidine Kinase in the Cytosol of Regenerating Rat Liver1

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Abstract
Two forms (Peak A and Peak B) of thymidine kinase [EC 2.7.1. 75] from regenerating rat liver cytosol were resolved and partially purified by DEAE-cellulose chromatography. Both fractions were identical with respect to their substrate requirement, pH optima, metal requirements, and molecular weight, as judged by their sedimentation in sucrose density gradient centrifugation. Peak B differed from Peak A in heat sensitivity, inhibition by dCTP and Km for thymidine and ATP. Peak B enzyme was the only enzyme found in normal adult liver and Peak A enzyme was the form increasing predominantly in regenerating liver.