2,6-dichloro-phenol indophenol prevents switch-over of electrons between the cyanide-sensitive and -insensitive pathway of the mitochondrial electrontransport chain in the presence of inhibitors

To evolve a simple oxygen electrode-based method to estimate alternative re spiration, one needs to develop a procedure to prevent switch-over of elect rons to either pathway upon inhibition by cyanide or salicylhydroxamic acid , It was hypothesized that the inclusion of appropriate electron acceptor, possessing redox potential close to one of the electron transport carriers in between ubiquinone (branch point) and cytochrome alpha-alpha(3), should be able to stop switch-over of electrons to either pathway by working as an electron sink. To test the hypothesis, 2,6-dichloro-phenol indophenol (DCP IP; redox potential +0.217 V), an artificial electron acceptor having a red ox potential quite similar to the site near cytochrome c(1) (redox potentia l +0.22 V) on the cyanide-sensitive pathway, was used with isolated mitocho ndria and leaf discs in the absence and presence of inhibitors (potassium c yanide, antimycin A, and salicylhydroxamic acid). Polarographic data confir med electron acceptance by DCPIP only from the inhibited (by cyanide or sal icylhydroxamic acid) mitochondrial electron transport chain, hence preventi ng switch-over of electrons between the cyanide-sensitive and cyanide-insen sitive pathway of respiration. Results with antimycin A and reduction statu s of DCPIP further confirmed electron acceptance by DCPIP from the mitochon drial electron transport chain. Possible implications of the results have b een discussed. (C) 1999 Academic Press.