Characterization of partially purified cytosolic protein-tyrosine kinase from porcine spleen.

Biochemical properties of a cytosolic protein-tyrosine kinase (CPTK-40) partially purified from porcine spleen were characterized and compared with p40 kinase, a cytosolic protein-tyrosine kinase from bovine thymus. When CPTK-40 was incubated with MnCl2 and (gamma-32P)ATP, only a phosphoprotein with a molecular weight of 40 kilodalton was observed. CPTK-40 efficiently phosphorylated tubulin with the rate of 0.5 nmol/min/mg. Unlike p40 kinase, casein was also a substrate for CPTK-40. Among various divalent cations tested, Co2+, Mn2+ and Mg2+ were effective metal ions for the enzyme activity. Ca2+ could also serve as a divalent cation for the activity although the rate was low. These results suggest that CPTK-40 is similar but not identical to p40 kinase.