Interaction between ubiquinone and ATPase in mitochondrial membranes.

The extraction of ubiquinone from mitochondrial membranes produces alterations of ATPase activity including a reversible loss of oligomycin sensitivity which is restored by long-chain Q-homologs, Short-chain ubiquinones like Q3 produce a loss of oligomycin and dicyclohexyl carbodiimide (DCCD) sensitivity in submitochondrial particles. The effect shows uncompetitive or noncompetitive Kinetics with respect to oligomycin or DCCD respectively. Long-chain ubiquinones have a competitive effect with Q3, thus restoring oligomycin sensitivity; they behave, however, in about the same way as Q3 in lowering the DCCD sensitivity in submitochondrial particles. On the basis of these observations we suggest that ubiquinone may be a physiological modulator of ATPase activity in the mitochondrial membrane.