Respiration-independent Binding of SR to Bean Mitochondria

Binding of Sr(2+) to bean mitochondria (Phaseolus vulgaris) shows a dissociation constant of 25 x 10(-6) and results in 40 to 50 nmoles of Sr(2+) bound per mg protein. The binding is partially inhibited by valinomycin plus K(+), 2, 4-dinitrophenol, as well as ruthenium red at a level of the 120 nmoles per mg protein. These compounds also partially inhibit active uptake of Sr(2+). Calcium and Mg(2+) also partially inhibit binding in the same magnitude as previously reported for inhibition of transport. Phosphate which is required for divalent cation transport is without effect on the binding of Sr(2+). The possible role of the observed binding sites in divalent cation transport is discussed.