Comparison of the ATPase Activities of Bovine Heart and Liver Mitochondrial ATP Synthases with Different Tissue-Specific γSubunit Isoforms

The kinetics of heart and liver mitochondrial ATPase (FoF 1) were examined using submitochondrial particles (SMPs) purified from the two tissues to obtain information on the role of γ subunit isoforms. The F 1 portion is mainly composed of the catalytic, common αβ subunits and tissue-specific γ subunits. In contrast to the previous reports on the kinetics and crystallography of various F 1′s, the Vmax and Km of the two isoforms of FoF 1 were identical although the SMPs were prepared from different tissues. Moreover sodium azide inhibited the two equally. The ATPase activity of liver SMP showed slightly steeper pH-dependency than that of heart SMP but the pH optima of the two were the same (pH 8).