Cytochrome c

Cytochrome c (CYCS) is a small, highly conserved electron carrier protein essential for mitochondrial respiration and apoptotic signaling (UniProt: P99999). It accepts electrons from cytochrome c1 and transfers them to cytochrome oxidase, thereby completing the final step of the mitochondrial electron-transport chain. Additionally, cytochrome c plays a critical role in programmed cell death: release of cytochrome c from mitochondria into the cytosol following pro-apoptotic signals triggers caspase-9 activation and downstream apoptotic cascades.

Cytochrome c is localized to mitochondria and participates in bioenergetic and cell-death pathways. In UniProt, cytochrome c is associated with Thrombocytopenia 4 (THC4; MIM 612004), a hematologic disorder, though this appears unrelated to its neurobiological roles (UniProt: P99999).

Cytochrome c is downregulated in Alzheimer's Disease brain tissue (Chaparral AD proteomics). Analysis of post-mortem AD brain versus age-matched controls revealed a mean log2 fold-change of −0.548 across measured subcellular fractions in TMT-labeled proteomic analysis. This reduction may reflect compromised mitochondrial function and altered energy metabolism characteristic of AD pathology.