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 channels can provide an aqueous pathway through the hydrophobic environment of the membrane. The MCC (multiple conductance channel) and PSC (peptide-sensitive channel) are two high-conductance channels previously identified in electrophysiological studies of mitochondrial membranes. MCC and PSC are the putative pores of the import complexes of the inner and outer membranes, respectively. The genetic, biochemical, and biophysical evidence regarding these assignments are summarized herein. These findings support the identification of MCC and PSC as the protein import channels of mitochondria.