Electron carrier protein. The oxidized form of the cytochrome c heme group can accept an electron from the heme group of the cytochrome c1 subunit of ubiquinol-cytochrome c oxidoreductase. Cytochrome c then transfers this electron to the dinuclear copper A center (CU(A)) of the COX2 subunit of cytochrome oxidase, the final protein carrier in the mitochondrial electron-transport chain. Isoform 1 (CYC1) is the predominant cytochrome c during aerobic/normoxic growth. Binds 1 heme c group covalently per subunit. By oxygen at the level of transcription. Expression drops rapidly when the oxygen concentration falls below 0.5 uM O(2). Methylation may enhance its transport into mitochondria. Methylation occurs in fungi, plants, and some protozoa, but not in animals. The precise role of methylation at Lys-79 is unknown, but it seems to preclude pro-apoptotic activity, possibly by lowering affinity for APAF1. Present with 7330 molecules/cell in log phase SD medium. Belongs to the cytochrome c family. Life shuttle - Issue 76 of November 2006