Adenosine diphosphate production from adenosine triphosphate by rat myofibrils: Inhibition by relaxing factor granules

Abstract

The adenosine triphosphatase activity of rat skeletal muscle myofibrils as measured by the utilization of adenosine triphosphate and the production of inorganic phosphate and adenosine diphosphate is markedly inhibited by rat muscle relaxing factor granules in the presence of 5 mM oxalate. With fresh myofibrils a moderate degree of inhibition of adenosine triphosphatase as measured by these three criteria is obtained with granules alone although full activity requires oxalate in addition. With aged myofibrils oxalate must be added to the reaction mixture in addition to granules to obtain inhibition of adenosine triphosphate uptake and inorganic phosphate production. In contrast, adenosine diphosphate production is inhibited by granules alone. This observation and certain other findings are interpreted as indicating separate pathways for the formation of inorganic phosphate and adenosine diphosphate by myofibrils and selective inhibition of the adenosine diphosphate producing pathway by granules.