Phospholipid-sensitive Ca2+-dependent protein kinase was partially purified from total particulate fraction of pig testis. The enzyme phosphorylated high mobility group 1 protein (HMG 1), one of the major chromatin-associated non-histone proteins. Other HMG proteins (HMG 2, 14 and 17) were not phosphorylated by the enzyme. Exhaustive phosphorylation of HMG 1 revealed that 1 mol of phosphate was incorporated/mol of HMG 1. The apparent Km value for HMG 1 was 3.66 microM. 1,3-Diolein stimulated the phosphorylation at 10 microM-Ca2+ in the presence of phosphatidylserine. The phosphorylation of HMG 1 was inhibited by adriamycin, an inhibitor of spermatogenesis.
Phosphorylation of high-mobility-group proteins by the calcium-phospholipid-dependent protein kinase and the cyclic AMP-dependent protein kinase.
