Abstract
The effects of inhibitors on the reduction of the bis-heme cytochrome b of ubiquinol: cytochrome c oxidoreductase (complex III, bc1 complex) has been studied in bovine heart submitochondrial particles (SMP) when cytochrome b was reduced by NADH and succinate via the ubiquinone (Q) pool or by ascorbate plus N,N,N', N'-tetramethyl-p-phenylenediamine via cytochrome c1 and the iron-sulfur protein of complex III (ISP). The inhibitors used were antimycin (an N-side inhibitor), beta-methoxyacrylate derivatives, stigmatellin (P-side inhibitors), and ethoxyformic anhydride, which modifies essential histidyl residues in ISP. In agreement with our previous findings, the following results were obtained: (i) When ISP/cytochrome c1 were prereduced or SMP were treated with a P-side inhibitor, the high potential heme bH was fully and rapidly reduced by NADH or succinate, whereas the low potential heme bL was only partially reduced. (ii) Reverse electron transfer from ISP/c1 to cytochrome b was inhibited more by antimycin than by the P-side inhibitors. This reverse electron transfer was unaffected when, instead of normal SMP, Q-extracted SMP containing 200-fold less Q (0. 06 mol Q/mol cytochrome b or c1) were used. (iii) The cytochrome b reduced by reverse electron transfer through the leak of a P-side inhibitor was rapidly oxidized upon subsequent addition of antimycin. This antimycin-induced reoxidation did not happen when Q-extracted SMP were used. The implications of these results on the path of electrons in complex III, on oxidant-induced extra cytochrome b reduction, and on the inhibition of forward electron transfer to cytochrome b by a P-side plus an N-side inhibitor have been discussed.
Highlights
The effects of inhibitors on the reduction of the bisheme cytochrome b of ubiquinol: cytochrome c oxidoreductase has been studied in bovine heart submitochondrial particles (SMP) when cytochrome b was reduced by NADH and succinate via the ubiquinone (Q) pool or by ascorbate plus N,N,N,Ntetramethyl-p-phenylenediamine via cytochrome c1 and the iron-sulfur protein of complex III (ISP)
This reverse electron transfer was unaffected when, instead of normal SMP, Q-extracted SMP containing 200-fold less Q (0.06 mol Q/mol cytochrome b or c1) were used. (iii) The cytochrome b reduced by reverse electron transfer through the leak of a P-side inhibitor was rapidly oxidized upon subsequent addition of antimycin
We have shown recently in energized submitochondrial particles (SMP) that reverse electron transfer from ISP/c1 to cytochrome b is inhibited more by antimycin, which binds near bH, than by myxothiazol, which binds near bL [13]
Summary
The effects of inhibitors on the reduction of the bisheme cytochrome b of ubiquinol: cytochrome c oxidoreductase (complex III, bc1 complex) has been studied in bovine heart submitochondrial particles (SMP) when cytochrome b was reduced by NADH and succinate via the ubiquinone (Q) pool or by ascorbate plus N,N,N,Ntetramethyl-p-phenylenediamine via cytochrome c1 and the iron-sulfur protein of complex III (ISP). We have shown that when SMP were treated with antimycin, KCN, and ascorbate plus TMPD to reduce the high potential centers of complex III, subsequent addition of NADH or succinate resulted in rapid and complete reduction of bH, and only the reduction of bL became slow and partial when ISP/c1 were prereduced [14].
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have