Cytochrome b-c1 complex subunit 2, mitochondrial

UQCRC2 (Cytochrome b-c1 complex subunit 2, mitochondrial) is a core component of the ubiquinol-cytochrome c oxidoreductase complex (Complex III) within the mitochondrial electron transport chain (UniProt: P22695). It catalyzes electron transfer from ubiquinol to cytochrome c while promoting proton translocation across the inner mitochondrial membrane, thereby coupling redox reactions to the proton gradient that drives ATP synthesis. UQCRC2 is also implicated in the proteolytic maturation of other Complex III subunits.

UQCRC2 is expressed in tissues with high metabolic demand. Pathogenic variants cause mitochondrial complex III deficiency, nuclear type 5 (MC3DN5; MIM 615160), characterized by neurological dysfunction, developmental delay, ataxia, and multi-system organ involvement (UniProt: P22695).

In Alzheimer's disease, UQCRC2 shows an ambiguous direction of change across subcellular fractions from post-mortem AD brain relative to age-matched controls, with a mean log2 fold-change of 0.44 (Chaparral AD proteomics). This modest and directionally inconsistent signal across fractions suggests either region-specific or compartment-specific dysregulation of mitochondrial Complex III in AD pathology.