Uptake of Adenine Nucleotides by Respiring Mitochondria during Active Accumulation of Ca++ and Phosphate.

The large scale, respiration-linked accumulation of Ca+f ions by isolated mitochondria (l-lo), which leads to deposition of amorphous granules of calcium phosphate (5, 7, 8, lo-12), has been found to be accompanied by accumulation of significant amounts of a phosphate derivative (or derivatives) hydrolyzed to inorganic phosphate by boiling in 1 N HCl for 7 minutes (5). In this paper it is demonstrated that the acid-labile phosphate accumulating with Ca++ and inorganic phosphate is contributed largely by adenosine diand triphosphates, which are accumulated from the medium in amount,s far exceeding the normal mitochondrial content of these nucleotides. The binding or accumulation of ADP and ATP by mitochondria is both proportional and parallel to the accumulation of Ca+f and phosphate; it shares with it similar cofactor requirements and sensitivity to inhibitors of respiration and phosphorylation. The data presented here show that the accumulation of adenine nucleotides is related to the requirement for ATP for supporting mitochondrial accumulation of Ca++ in the presence of phosphate (2, 13). It is also shown that the accumulation of adenine nucleotides during uptake of Ca++ and phosphate, measured under conditions in which there is no significant damage to mitochondria by excess Ca++, is essentially completely inhibited by atractyloside but not affected by oligomycin. Some of the data reported in this paper were presented in a preliminary communication (14).