Sulfide:quinone oxidoreductase, mitochondrial

Sulfide:quinone oxidoreductase (SQOR) is a mitochondrial enzyme that catalyzes the oxidation of hydrogen sulfide using quinone cofactors such as ubiquinone-10, producing thiosulfate and sulfane intermediates. The reaction requires an additional electron acceptor; glutathione is believed to serve this role in vivo (UniProt: Q9Y6N5). SQOR localizes to the inner mitochondrial membrane and participates in hydrogen sulfide detoxification, a critical pathway for cellular redox balance.

Mutations in SQOR cause sulfide:quinone oxidoreductase deficiency (SQORD), an autosomal recessive mitochondrial disorder featuring variable severity from asymptomatic presentation to fatal encephalopathy with Leigh syndrome-like features, lactic acidosis, and impaired respiratory chain complex IV activity (UniProt: Q9Y6N5). The protein's role in bioenergetics and oxidative stress management links it to neurodegenerative contexts.

In Alzheimer's Disease, SQOR is upregulated in post-mortem AD brain tissue relative to age-matched controls (mean log2FC = 0.51, Chaparral AD proteomics). This elevation may reflect compensatory mitochondrial adaptation to oxidative stress or altered hydrogen sulfide metabolism in the AD brain, though the functional consequence remains to be determined.