ISOLATION AND PROPERTIES OF CA-2+-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 increased the conductivity of membranes by 3-4 orders. Transmembrane Ca2+ gradient indices 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).