MODULATION OF RAT-BRAIN CALPASTATIN EFFICIENCY BY POSTTRANSLATIONAL MODIFICATIONS

Calpains, the thiol proteinases of the calcium-dependent proteolytic s ystem, are regulated by a natural inhibitor, calpastatin, which is pre sent in brain tissue in two forms, Although both calpastatins are high ly active on human erythrocyte calpain, only one form shows a high inh ibitory efficiency with both rat brain calpain isozymes, The second ca lpastatin form is almost completely inactive against homologous protei nases and can be converted into an active one by exposure to a phospho protein phosphatase, also isolated from rat brain, Phosphorylation of the active calpastatin by protein kinase C and protein kinase A promot es a decrease in its inhibitory efficiency, The interconversion betwee n the two inhibitor forms seems involved in the adjustment of the leve l of intracellular calpastatin activity on specific cell requirements. (C) 1997 Federation of European Biochemical Societies.