Beef heart mitochondrial adenosine triphosphatase-catalyzed formation of a transition state analog in ATP synthesis

The mechanism of beef heart mitochondrial ATPase (F1) was studied using chromium(III)-substituted substrate analogs. Incubation of F1 with monodentate Cr(III)ADP and 32Pi followed by chromatography on Sephadex G-25 resulted in 32Pi counts in the F1 protein peak. The appearance of radioactivity from inorganic phosphate in the protein peak was dependent upon the presence of monodentate Cr(III)ADP and F1, and was inhibited by MgADP. Removal of the enzyme from the reaction mixture containing Cr(III)ADP and 32Pi by acid precipitation followed by chromatography on Sephadex G-10 indicated the net formation and slow release of a radioactive product. High voltage electrophoresis showed that this product was 32Pi . Cr(III)ADP. Incubation of F1 with bidentate Cr(III)ATP also resulted in formation of this product. These results indicated that non-membrane-bound F1 was capable of net synthesis of what may be an ATP synthesis and hydrolysis transition state analog. The F1-dependent formation of the complex was taken as evidence that the soluble ATPase can function in ATP synthesis as well as ATP hydrolysis.