Studies on oxidative phosphorylation: XV. Latent adenosine 5′-triphosphatase activity of factor A

Abstract

Further purification and stabilization of the mitochondrial energy transfer factor, Factor A, is described. The eleetrophoretic purity and sedimentation properties of Factor A are shown. Purified Factor A exhibits characteristic activation of ATPase at 45 ° and cold lability of the resulting ATPase activity. Activity in energy-linked reactions is unaffected during the treatment. Heating and cooling cycles are associated with gross changes in the optical rotatory dispersion (ORD) at 232 mμ. However, the time course of ATPase activation and ORD changes are quite different. An ATPase inhibitor and ADP are recovered from Factor A following denaturation of the material at 75 dg. Activation of oligomycin-insensitive ATPase by exposure to elevated temperatures (45–60 °) has been observed in submitochondrial particles also. This ATPase remains bound to particles and declines on cooling. It is proposed that the ADP phosphorylation enzyme of mitochondria is devoid of ATPase activity unless it is exposed to environmental changes.