Further studies on the requirement for phosphate for the oxidation of glutamate by rat-liver mitochondria in the presence of dinitrophenol

Abstract

1.1. The oxidation of glutamate by rat-liver mitochondria in the presence of dinitrophenol and absence of added phosphate acceptor has been studied.2.2. When the concentration of added inorganic phosphate was 50 μM or lower, the oxidation declined rapidly after about 10–15 min. Respiration could be restored by adding inorganic phosphate.3.3. In the absence of added phosphate, the inorganic phosphate initially present in the mitochondrial suspension disappeared slowly and an almost constant rate. The P:O ratio was 0.01–0.015.4.4. In the absence of added phosphate, the oxidation of glutamate was further inhibited by AMP, but not by ADP. AMP had no effect in the presence of a sufficiently high concentration of added phosphate, and the inhibition by AMP could be relieved by the subsequent addition of phosphate.5.5. It is concluded that in addition to the reaction of inorganic phosphate with endogenous ADP, catalysed by the substrate-linked phosphorylation reaction, and the hydrolysis of the ATP formed by the dinitrophenol-induced ATPase, there is a side reaction which slowly leads to the disappearance of inorganic phosphate.