Problems in the experimental determination of substrate-specific H+/O ratios during respiration

Krab et al. (1984) have recently tried to resolve the long-standing controversy as to whether the mechanistic H+/O coupling ratio for electrons passing through sites II and III of the mammalian electron transport chain to O2 is 6 or 8. Using a mathematical model they concluded that the higher number reported by Costa et al. (1984) was an overestimate because of the unaccounted for delayed response of the O2 electrode. Responding to criticisms of Lehninger et al. (1985), they have recently used (Krab and Wikström, 1986) an improved mathematical model which shows that the higher number found by Costa et al. was probably due to an inadequate accounting for the effects of the proton leak process which accompanies the translocation process. The impression is left that the situation is now resolved in favor of the lower number. We agree that the procedures of Costa et al. do not properly account for the leak process, and provide further evidence in this paper of the magnitude of the problem. However, we disagree that the number 6.0, favored by Wikström et al., rests on any more solid experimental support. We provide evidence here for this conclusion and raise the question as to whether or not any unique, fixed, integral number exists for the H+/O ratio accompanying the oxidation of a particular substrate.