Summary: A soluble protein kinase from the promastigote form of the parasitic protozoon was partially purified using DEAE-cellulose, Sephadex G-200 and phosphocellulose columns. The enzyme preferentially utilized protamine as exogenous phosphate acceptor. The native molecular mass of the enzyme was about 85 kDa. Mg ions were essential for enzyme activity; other metal ions, e.g. Ca, Co, Zn and Mn, could not substitute for Mg. cAMP, cGMP, Ca/calmodulin and Ca/phospholipid did not stimulate enzyme activity. The pH optimum of the enzyme was 7.0-7.5, and the temperature optimum 37.C. The apparent for ATP was 60 μM. Phosphoamino acid analysis revealed that the protein kinase transferred the γ-phosphate of ATP to serine residues in protamine. The thiol reagents -hydroxymercuribenzoic acid, 5-5′-dithio-bis(2-nitrobenzoic acid) and -ethylmaleimide inhibited enzyme activity; the inhibition by -hydroxymercuribenzoic acid and 5-5′-dithio-bis(2-nitrobenzoic acid) was reversed by dithiothreitol.


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