Effect of hydroxy analogs of coenzyme Q on DPNH- and succin-oxidase activities of yeast mitochondria

2,3-Dimethoxy-5-hydroxy-6-phytyl-and-6-farnesyl-1,4-benzoquinones (HPB and HFB) inhibit DPNH- and succin-oxidases of intact mitochondria from yeast. CoQ 2 reversed the inhibition in DPNH-oxidase, but there was little or no reversal in succin-oxidase. CoQ 6, the dominant CoQ of yeast, showed the same relative reversals as CoQ 2. For CoQ 6-deficient DPNH-oxidase, supplementation with: (a) HPB; (b) HFB; (c) HPB and CoQ 6; (d) HPB and CoQ 10 showed unexpected increases in activity indicating coenzymatic activity for HPB and HFB; the inhibitory effects of HPB and HFB were apparent with supplementation with CoQ 2. HPB inhibited the CoQ 6-deficient succin-oxidase, and also in the presence of CoQ 2, CoQ 6 or CoQ 10.