Monoclonal antibodies against type II rat brain protein kinase C

Monoclonal antibodies (8/1, 10/10, and 25/3) against rat brain type II protein kinase C were used for the immunochemical characterization of this kinase. These antibodies immunoprecipitated the type II protein kinase C in a dose-dependent manner but did neither to the type I nor III isozyme. Immunoblot analysis of the tryptic fragments from protein kinase C revealed that all three antibodies recognized the 27-38-kDa fragments, the phospholipid/phorbol ester-binding domain, but not the 45-48-kDa fragments, the kinase catalytic domain. The immune complexes of the kinase and the antibodies retained 70-80% of the kinase activity which was dependent on Ca2+ and phosphatidylserine and further activated by diacylglycerol or tumor-promoting phorbol ester. With antibody 8/1, the kinetic parameters with respect to Km for ATP and histone and K alpha for phosphatidylserine and phorbol 12,13-dibutyrate were not significantly influenced. However, the antibody causes variable effects on the K alpha for Ca2+ under different assay conditions. When determined in the presence of phosphatidylserine, the K alpha for Ca2+ was reduced by an order of magnitude (37 +/- 8 to 2.0 +/- 1.8 microM); in the presence of phosphatidylserine and phorbol 12,13-dibutyrate, the K alpha for Ca2+ was not significantly altered; and in the presence of phosphatidylserine and dioleoylglycerol, the kinase became an apparently Ca2+-independent enzyme. The effects of antibody 8/1 on the kinetic parameters of the enzyme for phorbol ester binding were different from those for kinase activity. This antibody causes a 20-30% reduction in phorbol ester binding and a 2-fold increase (1.9 +/- 0.2 to 3.9 +/- 0.3 micrograms/ml) in the concentration of phosphatidylserine required for half-maximal binding, but is without significant influence on those parameters for Ca2+ and phorbol 12,13-dibutyrate. The differential effects of antibody 8/1 on kinase activity and phorbol ester binding with respect to the kinetic parameter of phosphatidylserine suggest that the roles of this phospholipid in supporting phorbol ester binding and kinase activation are different. In the presence of the antibody, the autophosphorylations of the phospholipid/phorbol ester-binding domain and the kinase domain were reduced; the reduction was more pronounced for the former than for the latter. These results suggest that the epitope for antibody 8/1 is localized within the phospholipid/phorbol ester-binding domain at the region adjacent to the kinase domain so that the autophosphorylations of both domains are affected.