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.