PHOSPHORYLATION AND ACTIVATION OF PROTAMINE KINASE BY 2 FORMS OF A MYELIN BASIC-PROTEIN KINASE FROM EXTRACTS OF BOVINE KIDNEY CORTEX

Two myelin basic protein kinases designated MBPK-1 and MBPK-2 were pur ified to apparent homogeneity from extracts of bovine kidney cortex. T he purified preparations exhibited an apparent M(r) almost-equal-to 40 ,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and approximately 42,000 (MBPK-1) and 45,000 (MBPK-2) by gel permeation ch romatography. Up to 0.4 and 1.8 mol of phosphoryl groups were incorpor ated per mol of MBPK-1 and MBPK-2, respectively, on threonines followi ng incubation with ATP. Autophosphorylation, incubation with protein p hosphatase 2A2 (PP2A2), CD45, or T-cell protein tyrosine phosphatase d id not affect MBPK-1 activity. Autophosphorylation increased by about 3-fold MBPK-2 activity. This autophosphorylation and activation was re versed by PP2A2 but not by CD45 or T-cell protein tyrosine phosphatase . MBPK-1 and MBPK-2 displayed a positive reaction with an antibody to mitogen-activated protein kinase. Purified preparations of protamine k inase were activated by about 1.5-6-fold and, after inactivation with PP2A2, were reactivated by about 30% by MBPK-1 and MBPK-2. Activation and reactivation correlated with the incorporation, respectively, of 0 .1-0.5 and 0.5 mol of phosphoryl groups/mol of the protamine kinase on serines. The results show that MBPK-1 and MBPK-2 are protamine kinase -activating kinases and suggest that MBPK-1 and MBPK-2 may be related to mitogen-activated protein kinase.