MCC and PSC, the putative protein import channels of mitochondria

All but a small fraction of the hundreds of proteins in a mitochondrion are synthesized in the cytoplasm and imported into the organelle. Water-filled channels are integral to the process of translocating proteins since chann els can provide an aqueous pathway through the hydrophobic environment of t he membrane. The MCC (multiple conductance channel) and PSC (peptide-sensit ive channel) are two high-conductance channels previously identified in ele ctrophysiological studies of mitochondrial membranes. MCC and PSC are the p utative pores of the import complexes of the inner and outer membranes, res pectively. The genetic, biochemical, and biophysical evidence regarding the se assignments are summarized herein. These findings support the identifica tion of MCC and PSC as the protein import channels of mitochondria.