The Effects of Guanidine and Alkylguanidines on the Energy Transfer Reactions of Mitochondria

(+)-alpha-(N-1-phenethyl) urea stereospecifically inhibits Ca2+ - but not ADP-stimulated mitochondrial respiration

The (+) isomer of alpha-(N-1-phenethyl) urea is a moderately potent inhibitor of Ca2+ -stimulated mitochondrial respiration of 45Ca2+ uptake (50 percent inhibition at 0.18 mM) while having no effect on adenosine diphosphate-stimulated respiration; the (-) isomer is without effect up to 4 mM. beta-Phenethylurea does not inhibit with either stimulus. The data support the involvement of a Ca2+ -specific protein in energized mitochondrial Ca2+ uptake.

On the mechanism of action of alkylguanidines on oxidative phosphorylation in mitochondria

The effect of octylguanidine and oligomycin on the oxygen uptake of rat liver mitochondria and on the ATPase activity of "sonic" submitochondrial particles has been studied. 1. Octylguanidine inhibits state 3 respiration with glutamate-malate and succinate as substrates, but much lower concentrations are required to inhibit oxygen uptake with the former substrates. State 4 respiration is unaffected by octylguanidine. 2. The titration-curve for the octylguanidine inhibition of glutamate-malate oxidation is hyperbolic and apparently biphasic, half-maximal inhibition is obtained at 30 muM octylguanidine. The octylguanidine-curve for inhibition of succinate oxidation is sigmoid with half-maximal inhibition at about 250 muM. 3. Octylguanidine and oligomycin show additive inhibitory action on state 3 respiration with both glutamate plus malage and succinate as respiratory substrates. 4. Concentrations of oligomycin or octylguanidine, which added separately are ineffective on state 3 respiration, become inhibitory when the two inhibitors are added together. 5. Octylguanidine inhibits the ATPase activity of sonic submitochondrial particles with a hyperbolic titration-curve analogous to that obtained for oligomycin inhibition. The inhibitory actions of octylguanidine and oligomycin on the ATPase activity are additive. 6. It is concluded that octylguanidine acts directly on the ATPase complex and that its binding at the action site is mutually exclusive with the binding of oligomycin. A kinetic explanation is given for the reported higher sensitivity of site I phosphorylation to octylguanidine.