Synthesis of ATP by soluble mitochondrial F 1 ATPase and F 1 –inhibitor‐protein complex in the presence of organic solvents

The F 1 and F 1 –inhibitor‐protein complex synthesized tightly bound ATP from ADP and P i when the organic solvents dimethylsulfoxide (20–50% v/v), ethyleneglycol (20–60% v/v) or poly(ethyleneglycol) 4000 and 8000 (30–50% w/v) were included in the assay media. There was no synthesis of tightly bound ATP in the absence of organic solvents. In the presence of 50% dimethylsulfoxide, maximal synthesis of ATP was obtained at pH values between 6.5 and 7.7. In both F 1 and F 1 ‐inhibitor‐protein there was no synthesis of ATP in the absence of MgCl 2 . The rate of ATP synthesis became faster as the MgCl 2 concentration in the medium was raised from 0.1–10 mM. The K m for P i of F 1 was in the range of 0.8–1.5 mM. The K m for P i of the F 1 ‐inhibitor‐protein was much higher than that of F 1 and could not be measured. In the presence of 10 mM MgCl 2 and 2 mM P i , the rate constants of ATP synthesis by F 1 and F 1 –inhibitor‐protein were 5.2–10.4 h −1 and 3.5–5.9 h −1 respectively. For both enzymes the rate constant of ATP hydrolysis was 0.69 h −1 . The tightly bound ATP of F 1 and F 1 ‐inhibitor‐protein were hydrolyzed at a much slower rate when either the P i concentration or the MgCl 2 concentration was suddenly decreased. Both in presence and absence of Mg 2+ , 40–60% of the radioactive tightly bound ATP synthesized by F 1 was hydrolyzed when non‐radioactive ATP was added to the assay medium. This was not observed when F 1 ‐inhibitor‐protein was used.