CARDIAC HIGH-MOLECULAR-WEIGHT CALMODULIN-BINDING PROTEIN CONTAINS CALPASTATIN ACTIVITY

A high molecular weight calmodulin binding protein (HMWCaMBP) was prev iously identified and purified from bovine heart cytosolic fraction [S harma, R. K. (1990) J. Biol. Chem. 265, 1152-1157]. In this study, we report the biological function of this protein, HMWCaMBP was subjected to peptide mapping and three peptides were sequenced, Two of the thre e peptide sequences were shown to be highly homologous to the calpain inhibitor, calpastatin, However, the third peptide did not show homolo gy to any known proteins, The Western blot analysis of HMWCaMBP and pu rified calpastatin from bovine cardiac muscle showed immunoreactivity with polyclonal antibody raised against HMWCaMBP. Furthermore, HMWCaMB P inhibited calpain II and calpain I activities in a dose dependent fa shion, Our data based on sequence homology, amino acid analysis, antib ody reactivity and calpain inhibition suggests that HMWCaMBP is homolo gous to calpastatin and may be a CaM-binding form of calpastatin.