Degradation of protein kinase M alpha by mu-calpain in a mu-calpain-protein kinase C alpha complex

In previous studies, we isolated and identified a mu-calpain-PKC alpha comp lex from rabbit skeletal muscle. At the same time we pointed out that an as sociation between mu-calpain and PKC alpha could occur at the level of the plasma membrane of muscle cells, and that PKC alpha could thus be considere d as a potential mu-calpain substrate. In the present study, using the mu-c alpain-PKC alpha complex as a model, we report that mu-calpain is activated in the combined presence of physiological calcium concentrations (less tha n 1 mu M) and phosphatidylserine. Furthermore our data also show that: (1) there exists a correlation between the appearance of autolyzed mu-calpain f orms and PKC alpha hydrolysis which leads to the formation of PKM alpha; (2 ) in certain experimental conditions, autolyzed mu-calpain forms are able t o hydrolyze PKM alpha independently of the presence of diacylglycerol. (C) 1999 Elsevier Science B.V. All rights reserved.