Open AccessThe stoichiometry of charge translocation by cytochrome oxidase and the cytochrome bc 1 complex of mitochondria at high membrane potential
Author(s) -
MURPHY Michael P.,
BRAND Martin D.
Publication year - 1988
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1988.tb14047.x
Subject(s) - cytochrome c oxidase , stoichiometry , cytochrome , electron transport chain , cytochrome c , electron transport complex iv , membrane , cytochrome c1 , coenzyme q – cytochrome c reductase , chemistry , cytochrome b , oxidase test , mitochondrion , biochemistry , enzyme , mitochondrial dna , gene
The q + /2e stoichiometries (number of charges translocated per electron pair transferred) of cytochrome oxidase and the cytochrome bc 1 complex in rat liver mitochondria were determined at a range of membrane potentials up to 180 mV. The method used was similar to the one used in the preceding paper by us in this journal to determine the q + /O stoichiometry of the mitochondrial electron transport chain from succinate to oxygen. The measured q + /2e stoichiometry of cytochrome oxidase was 3.5 positive charges per O atom reduced at low membrane potential (120 mV) and it decreased to about 1.5 at high membrane potential (180 mV). The measured q + /2e stoichiometry of the cytochrome bc 1 complex was between 1 and 1.25 positive charges ejected per electron pair and did not change significantly as ΔΨ was varied from 85 mV to 157 mV. The sum of the q + /2e stoichiometries of cytochrome oxidase and the cytochrome bc 1 complex determined separately was similar to their value determined together for electron transport from succinate to oxygen over the range of membrane potentials studied. The most probable interpretation of these results is that the stoichiometry of the cytochrome bc 1 complex is invariant over a range of membrane potentials and that the q + /2e stoichiometry of cytochrome oxidase decreases from 4 at low membrane potential to 2 at high membrane potential.