Inhibition of Electron and Energy Transfer in Mitochondria

Conventional determinations of the effect of uncoupling agents on osidative phosphorylation have usually been obtained in terms of the diminution of the P :0 ratio’ (l-3). When tightly coupled preparations are used, it is possible to determine the effect of the uncoupling agent in terms of the diminution of the respiratory control ratio (4-6). With spectroscopic methods, it is similarly possible to titrate the steady state oxidation-reduction level of the respiratory carriers with the uncoupling agent; cytochrome b and reduced pyridine nucleotide are particularly easy to measure (7-9). Similarly, a low concentration of azide allows a titration of cytochrome a or c with the uncoupling agent (8-10). All such methods measure the effect of the uncoupling agent on the steady state values of the P:O ratio, the respiratory control ratio, or the oxidation-reduction level of the respiratory pigments. There are two similar equations for the reduction of mitochondrial pyridine nucleotide in an energy-linked reaction in the presence of succinate (11).