Citazione:

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numbers between two and four were reported for the H+/ATP ratio, which is the number of protons transported through the enzyme per ATP synthesized (Schwartz, 1968; Junge et al., 1970; Hangarter and Good, 1982; Mills and Mitchell, 1982; Davenport and McCarty, 1984; Strotmann and Lohse, 1988; Van Walraven et al., 1996).

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Citazione:

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The H+/ATP ratio, defined as the number of protons necessary to synthesize one ATP at equilibrium, is four, according to the data of the present work. Given the stoichiometry of three beta-subunits per CF0F1 and the stoichiometry of 14 subunits III per CF0F1, as recently determined in isolated subunit III complexes (Seelert et al., 2000; Müller et al., 2001), their ratio becomes 14/3 approximately 4.7. This difference might indicate that the stoichiometric ratio of subunits does not represent the H+/ATP ratio, or that the subunit stoichiometry in the isolated subunit III-ring is different from that in intact CF0. As has been pointed out previously (Ferguson, 2000; Seelert et al., 2000; Stock et al., 2000), the H+/ATP ratio might vary between different species. A value of 4 for the mitochondrial enzyme would result in a P/O ratio of 2 for NADH oxidation and 1.2 for succinate oxidation, in striking contrast to the experimentally determined values of 2.5 and 1.5, respectively, which agree instead with an H+/ATP of 3. As those authors emphasize, the ratio between 3 and 4 H+/ATP is very similar to the ratio of 10 to 14 subunits c, as found in the mitochondrial (Stock et al., 2000) and chloroplast (Seelert et al., 2000) enzyme, respectively. However, as the data of the present work indicate, the issue of c/beta stoichiometry versus H+/ATP stoichiometry remains, thus far, still open. Therefore, for an understanding of how proton movement through F0 drives ATP synthesis in F1, both parameters, on one side the c-subunit stoichiometry and on the other side the H+/ATP ratio, need to be the subject of careful investigations in different species.

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