Cytochrome c binds to lipid domains in arrays of mitochondrial outer membrane channels.

Computer-averaged electron microscopic images of negatively stained crystalline arrays of fungal mitochondrial outer-membrane channels in the presence and absence of cytochrome c were compared. Neither the apo- nor the holo- forms of cytochrome c significantly changed the stain distribution in the protein regions of the channel arrays. However, both forms of cytochrome c caused significant stain exclusion from the lipid domains in the arrays, suggesting binding of the polypeptides at these loci. The implications of binding of apocytochrome c to clusters of exposed phospholipids on the mitochondrial outer membrane are discussed with respect to the mechanism of uptake of this polypeptide by mitochondria.