Synthesis of phosphocreatine and phosphoarginine by mitochondria from various sources

Mitochondria from heart, skeletal muscle and the liver of the rat have been shown to synthesise phosphoarginine through ATP if supplied with arginine and lobster arginine kinase. Liver mitochondria have been shown to synthesise phosphocreatine through ATP with the aid of the cytosolic isomer of creatine kinase. Mitochondria prepared from muscles of a crustacean, a fish and a bird have been shown oxidatively to synthesise phosphocreatine (crustacean) and phosphoarginine (fish and bird) provided they are supplied with the appropriate kinase and catalytic amounts of ATP. Within one second of the addition of either cytosolic kinases, mitochondria from skeletal muscle and liver begin a steady state synthesis of phosphoarginine or phosphocreatine. The results suggest that, with respect to phosphagen synthesis, the addition of the cytosolic enzymes can substitute for the mitochondrial enzyme. It is difficult therefore to accept a special vectorial function for the bound mitochondrial enzyme at the biological concentrations of ATP and the cytosolic enzymes normally associated with phosphagen synthesis.