Synthesis of Enzyme-Bound ATP by Mitochondrial Soluble F1-ATPase in the Presence of Dimethylsulfoxide1

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Abstract
We found that ATP is synthesized by mitochondrial soluble F 1 -ATP from medium ADP and P 1 in the presence of dimethylsulfoxide (DMSO), with the amount synthesized increasing with the DMSO concentration to a maximum at 30% (w/v) DMSO. In the presence of 35% (w/v) DMSO, ADP was scarcely converted into AMP and much more ATP was formed than AMP. The pH dependence curve of ATP synthesis was bell-shaped with the optimum at 6.7. The amount of synthesized ATP measured after stopping the reaction with trichloroacetic acid was almost equal to that measured after stopping the reaction with sodium dodecyl sulfate or with ethanol. Therefore, we measured the amount of ATP synthesized by F 1 from ADP and P 1 in the presence of 4.2 mM Mg 2+ and 35% (w/v) DMSO at pH 6.7 and 30°C after stopping the reaction with trichloroacetic acid. The following results were obtained.