PHOSPHATE AFFECTS THE DISTRIBUTION OF FLUX CONTROL AMONG THE ENZYMES OF OXIDATIVE-PHOSPHORYLATION IN RAT SKELETAL-MUSCLE MITOCHONDRIA

The flux control coefficients of adenine nucleotide translocase, the p hosphate transporter, and H+-ATPase were determined in rat skeletal mu scle mitochondria using glutamate plus malate as substrates and solubl e F1-ATPase as load enzyme. It was observed that the flux control coef ficients of adenine nucleotide translocase, H+-ATPase, and the load en zyme F1-ATPase, at comparable rates of respiration, strongly depend on the phosphate concentration in the incubation medium. So, the flux co ntrol exerted by adenine nucleotide translocase, in the intermediate s tates of mitochondrial respiration (approximately 120 nmol of O2/min/m g) at 10 mM phosphate, was found to be about 0.37. At a phosphate conc entration of 1 mM and comparable rates of respiration the flux control coefficient of the translocase decreased to about 0.20. Under these c onditions, a sharp increase in the controlling influence of H+-ATPase from 0.10 to 0.74 was detected. Furthermore, at this flux rate, the su m of flux control coefficients of adenine nucleotide translocase, H+-A TPase, phosphate transporter, and the load enzyme F1-ATPase was noted to be very close to unity. This indicates that under the conditions of intermediate state respiration, all of the other reactions have a neg ligible controlling influence on oxidative phosphorylation in skeletal muscle mitochondria.