Isolation and reactions of a phosphorylated form of phosphoryl transferase from beef heart mitochondria

Abstract

Phosphoryl transferase, a mitochondrial protein which increases the phosphorylative capacity of poorly phosphorylating submitochondrial particles and catalyzes an ATP-ADP exchange reaction, is phosphorylated during oxidation either of succinate or pyruvate-malate. Inhibitors of oxidative phosphorylation and electron transfer, as well as uncouplers of oxidative phosphorylation, inhibit the phosphorylation of the transferase when phosphorylation is mediated by electron transfer. The protein is also phosphorylated by ATP, the donor group being specifically the terminal phosphate of ATP. The transphosphorylation reaction is not inhibited by inhibitors of electron transfer and coupled phosphorylation, nor by uncouplers of oxidative phosphorylation. The phosphoryl form of the transferase can phosphorylate ADP in the presence of hexokinase, glucose, and magnesium ion, but the transfer is only 50% complete. During this transfer reaction a portion of the protein-bound phosphate becomes transformed to an acid-stable form. Phosphorus is released from phosphoryl transferase as inorganic orthophosphate at pH 4 and 10 and by heat, but is relatively stable at pH 7.5 at 0 °. Hydroxylamine also induces release of protein-bound phosphorus as inorganic phosphate. The possible role of the phosphoryl group of the transferase in oxidative phosphorylation is discussed.