Slipping proton pumps

In Fig. 1.4A we show a plot of what this relationship predicts for an experiment in which mitochondrial respiration is titrated away by the addition of respiratory inhibitor, for the case that q= -1 (no slip, dashed line) and cases in which -1 (slip, full lines). Pietrobon et al. [44, see also Refs. 46 and 47] have actually carried out this experiment and in Fig. 1.4B we reproduce their findings. It is clear that the experimental results are in line with the idea [44] that there is significant slip in the 

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Fig. 1.4. Slipping proton pumps. (A) Simulation of the relationship between electron transfer rate (Jg) and AgH for different degrees of coupling ( ) of an electron transferring proton pump. A/Ih expressed in units Z AGq. (B) Actual experimental results (from Ref. 44 with kind permission from the authors and the copywright owner) for different segments of the mitochondrial respiratory chain as proton pump. Both in (A) and in (B) the rate of electron transfer is varied through titration with an electron transfer inhibitor.

Fig. 3.7. Cubic model of a redox-linlced proton pump. OX and RED denote a redox centre in the oxidised and reduced state. The bar marked M or C next to OX and RED indicates an acidic group, the function of which is linked to the redox centre. M and C mean that the group is connected protonically either with the aqueous matrix or cytoplasmic phases, respectively. When the group is protonated the bar is supplemented with H. Left and right faces of the cube separate states in electronic and protonic contact with the input and output sides of the transducer, respectively. Allowed transitions between these are indicated by thick arrows. Dotted lines denote forbidden transitions. If the latter gain significant probability relative to allowed transitions proton transport becomes decoupled from electron transfer (so-called slipping ). (From Ref. 8.)...

In the model any dissipation is considered to occur both through leaks within a single coupling unit (this kind of energy dissipation within a protonic pump has been proposed previously as a slip of the pump (Pietrobon et al. 1981,1982)) and through leaks between the two bulk phases. According to this model the bulk-to-bulk results from the slow diffusion of... 

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