Enzymes which form pores in mitochondrial membranes that allow proteins synthesized in the cytosol to enter the organelle. Each mitochondrion imports about 1,000 different proteins. Translocases located in the outer membrane are called TOMs, while those of the inner membrane are called TIMs. The proteins that make up TOMs and TIMs are encoded by nuclear genes and are synthesized in the cytosol. So these precursor proteins must also be imported into the mitochondrion, sorted, and directed to their appropriate locations, where they are assembled into functioning enzymes. The outer mitochondrial membrane contains receptors that recognize those proteins of the cytosol destined to be internalized. These preproteins contain amino acid sequences to which the receptors bind. The preproteins collected by the receptors are then passed by the TOMs into the fluid-filled space between the membranes. Here appropriate preproteins are passed by TIMs into the mitochondrial matrix for further processing, while some are retained in the inner membrane.
Subjects: Genetics and Genomics.