Protonic sidedness of the binuclear iron-copper centre in cytochrome oxidase.

The oxidised (ferric-cupric) binuclear centre of cytochrome oxidase is converted into two other states, presumably ferrylcupric (F) and ferric-peroxy-cupric (P), by energy-dependent reversed electron transfer from the centre (and water) to cytochrome c [(1981) Proc. Natl. Acad. Sci. USA 78, 4051-4054; (1987) Chem. Scr. 27B, 53-58]. This sequence of events represents a partial reversal of the O2 reduction catalysed by the centre. Here it is shown that the strong pH-dependence of these reactions is exerted specifically from the matrix (M) side of the inner mitochondrial membrane. This proves unequivocally that the binuclear centre generates protonmotive force by means of its vectorial accessibility for electrons and protons.