Calcium binding to polypeptides of rat liver and Zajdela hepatoma mitochondrial inner membranes

Composition and amount of 45Ca 2+-binding proteins in the inner membrane fraction of rat liver and Zajdela hepatoma mitochondria were determined. In the inner membrane of liver mitochondria, three major 45Ca 2+-binding polypeptides: a protein of ∼130 kDa (carbamoyl-phosphate synthetase), a glycoprotein of 43–44 kDa (previously considered as the calcium uniporter), and 29–30 kDa protein were found. These components were absent (130 kDa component) or relatively reduced (43–44 kDa and 29–30 kDa components) in the inner membrane of hepatoma mitochondria. Previously unknown low molecular mass polypeptides, having very high Ca 2+-binding ability, were found in the inner membrane of hepatoma mitochondria. One of them might be the natural Ca 2+-binding inhibitor of H +-ATPase.