Water-filled channels are central to the process of translocating proteins since they provide aqueous pathways through the hydrophobic environment of membranes. The Tom and Tim complexes translocate precursors across the mitochondrial outer and inner membranes, respectively, and contain channels referred to as TOM and TIM (previously called PSC and MCC). In this study, little differences were revealed from a direct comparison of the single channel properties of the TOM and TIM channels of yeast mitochondria. As they perform similar functions in translocating proteins across membranes, it is not surprising that both channels are high conductance, voltage-dependent channels that are slightly cation selective. Reconstituted TIM and TOM channel activities are not modified by deletion of the outer membrane channel VDAC, but are similarly affected by signal sequence peptides.

No abstract

The respiratory uncouplers carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) affect the activities of two mitochondrial ion channels from mouse liver. At micromolar concentrations, the phenylhydrazones block the voltage-dependent 100-pS channel, mCS, and induce the multiple-conductance-level channel, MCC. The binding site(s) involved in perturbation of channel activities are probably distinct from the sites involved in uncoupling of oxidative phosphorylation which occurs at nanomolar concentrations of the phenylhydrazones. The effects of FCCP and CCCP on the mitochondrial ion channels could be partially reversed by washing with fresh media and were always reversed by perfusion with dithiothreitol. These results indicate that the effects of the phenylhydrazones on mitochondrial ion channels may be related to the ability of these compounds to act as sulfhydryl reagents and not to their protonophoric and uncoupling activity.