The effect of ribonuclease on the binding of calcium by mitochondria

Mitochondria, isolated from potato tuber, pretreated with ribonuclease (RNase) showed an increase in calcium binding at low enzyme concentration. The same dosage-response pattern was obtained whether the enzyme treatment was conducted for 10, 30 or 120 min. However, when the enzyme treatment was carried out at 0° instead of at 30°, no increase in Ca-binding was obtained, suggesting that no interaction occurred between the enzyme and the divalent cation. Oxygen consumption under the same conditions was not affected. Microsomes treated with RNase did not show a change in their Ca-binding capacity, although untreated microsomes showed about the same increase in Ca-binding with increase in temperature as did the mitochondria. When mitochondria prelabeled with (45)Ca, after extracting their inorganic calcium phosphate, were treated with RNase a liberation of Ca, ribonucleotide, and phosphate was observed. It is suggested that Ca ions form a bridge like bond between ribonucleic acid and either phospholipids or phospholipoproteins, because RNase liberated more phosphate than nucleotides and the extra phosphate cannot be inorganic calcium phosphate, since the calcium phosphate was extracted before addition of RNAse.