Cytochrome c oxidase subunit 5B, mitochondrial

COX5B (cytochrome c oxidase subunit 5B) is a 129-amino acid mitochondrial protein that functions as a component of complex IV in the electron transport chain. It participates in the final step of oxidative phosphorylation, where electrons from cytochrome c are transferred to molecular oxygen to generate water, coupled with proton pumping that drives ATP synthesis (UniProt: P10606).

COX5B is localized to the inner mitochondrial membrane and is expressed in tissues with high oxidative metabolic demand. The UniProt record does not list primary disease associations for this protein (UniProt: P10606).

COX5B is down-regulated in Alzheimer's disease brain tissue. Quantitative proteomics analysis of post-mortem AD brain versus age-matched controls detected reduced COX5B abundance with a mean log2 fold-change of −0.73 across mitochondrial and cytoplasmic fractions (Chaparral AD proteomics). This finding is consistent with mitochondrial dysfunction observed in AD pathology and suggests impaired oxidative capacity in affected brain regions.