Isolation of a low molecular weight Ca2+ carrier from calf heart inner mitochondrial membrane.

Abstract

A protein was isolated from calf heart inner mitochondrial membrane with the aid of an EPR assay based on the relative binding properties of Ca2+, Mn2+ and Mg2+ to the protein. The MW of this protein was estimated to be about 3000 by urea/sodium dodecyl sulfate gel elecrophoresis and amino acid analysis. The protein is shown to have 2 classes of binding sites for Ca2+ by flow dialysis studies and can extract Ca2+ into an organic phase. The selectivity sequence of this protein determined from the organic solvent extraction experiments shows that it favors divalent cations over monovalent cations. Also, the relative selectivity sequence for divalent cations is Ca2+, Sr2+ > Mn2+ > Mg2+. Ruthenium red and La3+ inhibit the protein-mediated extraction of Ca2+ into the organic solvent. The Ca translocation in a Pressman cell by this protein is selectively driven by a H ion gradient. Control experiment indicate that the Ca2+ transport properties of the protein are not due to the contaminating phospholipids. A Ca2+ carrier, now called caleiphorin, was isolated from the inner mitochondrial membrane.