Isolation and properties of Ca2+-transporting glycoprotein and peptide from beef heart mitochondria

The 40,000-dalton glycoprotein and 2000-dalton peptide inducing selective Ca²⁺-transport through bilayer lipid membranes were isolated from beef heart homogenate and mitochondria. Micromolar concentrations of these substances were found to increase the conductivity of membranes by 3–4 orders. Transmembrane Ca²⁺ gradient induces an electric potential difference whose magnitude is close to the theoretical for ideal Ca²⁺ selectivity. The inhibitor of mitochondrial Ca²⁺ transport, ruthenium red, abolishes both the glycoprotein-and peptide-induced Ca²⁺ transport in bilayer lipid membranes. Thiol groups essential for Ca²⁺ transport activity were revealed in the glycoprotein and peptide. Addition of these substances to rat liver mitochondria induces Ca²⁺-dependent inhibition of the state 3 respiration that can be released by uncouplers (oligomycin-like effect).