IN VITRO STUDIES OF P³² UPTAKE IN MOUSE LIVER MITOCHONDRIA

Isolated mouse liver mitochondria were incubated in two types of P³²-labelled sucrose-phosphate buffers. The first contained no added ATP or oxidizable substrate. The second contained added ATP. Samples were taken at specified times, up to 60 minutes, and analyses were made of the mitochondrial TCA-soluble inorganic P³² and the total mitochondrial residue P³¹ and P³². The results of the analyses showed that when the phosphorus inhibition index (the ratio of the amount of incubation inorganic phosphorus to the square of the amount of tyrosine in the mitochondria) was high, inorganic P³² uptake was low and vice versa. In accordance with established data, increased P³² uptake was obtained when ATP was added. ATP was found to stabilize the turnover of TCA-insoluble residue phosphorus as well as to maintain the TCA-soluble orthophosphate pool. These results support findings regarding the inhibitory and controlling effects of incubation medium phosphate in the regulation of inorganic phosphorus uptake.