Redox potentials and phosphorylative efficiency of mitochondria

In mitochondria which exhibit high P O ratios, > 5, P O ratios progressively increase during State 3 respiration. This is associated with progressive increases in the level of reduction of electron carriers, especially cytochrome C and flavin. With mitochondria whose P O ratio is 3 or less, all electron carriers are oxidized upon addition of ADP. Similarly with substrates of progressively decreasing redox potential, a parallel decrease in the steady-state level of reduction of the electron carriers also occurs. These data suggest that mitochondria, like chloroplasts, can phosphorylate efficiently only under conditions in which high levels of reduction of the electron carriers are maintained during State 3 respiration. These data are discussed in relation to the theory of the mechanism of phosphorylation previously proposed for chloroplasts.