Characterization of DNA Kinase from Calf Thymus

Abstract
DNA kinase has been purified to homogeneity from calf thymus. The purified enzyme, with a specific activity of 16.7 units/mg protein at 25° C, exhibited a sharp pH/activity curve with a pH optimum at 5.5 and low activity at alkaline pH. The molecular weight of the enzyme was estimated by dodecylsulfate/polyacrylamide gel electrophoresis to be 5.4 × 104. The enzyme has a sedimentation coefficient of 4.0 S. An apparent molecular weight of 5.6 × 104 and a Stokes' radius of 3.3 nm were estimated by gel-filtration on Sephadex G-100. The enzyme phosphorylates neither yeast RNA nor poly(A) instead of DNA. Compared with rat liver DNA kinase, calf thymus DNA kinase is relatively resistant to the inhibition by sulfate (Ki= 7 mM) and pyrophosphate (Ki= 5 mM). The enzyme activity is markedly stimulated by polyamines at the sub-optimal concentration of Mg2+ but not by monovalent cations.

This publication has 18 references indexed in Scilit: