Succinate dehydrogenase complex, subunit A, flavoprotein variant is a protein that in humans is encoded by the SDHAgene.
The succinate dehydrogenase (SDH) protein complex catalyzes the oxidation of succinate (succinate + ubiquinone => fumarate + ubiquinol). The SDHA subunit is connected to the SDHB subunit on the hydrophilic, catalytic end of the complex, and weighs 72.7 kDA. Electrons removed from succinate transfer to SDHA, transfer across SDHB to the SDHC/SDHD subunits on the hydrophobic end of the complex anchored in the mitochondrial membrane.
The gene that codes for the SDHA protein is nuclear, even though the protein is located in the inner membrane of the mitochondria. The location of the gene in humans is on the fifth chromosome at p15. The gene is partitioned in 15 exons. The expressed protein has 664 amino acids.
Mutations in the SDHA subunit have a distinct pathology from mutations in the SDHB/SDHC/SDHD subunits; it is the only subunit to never have shown tumor suppressor behaviour. Heterozygous carriers of an SDHA mutation do not develop paragangliomas as has been seen for mutations in the other subunits. This appears to be due to the expression of two similar SDHA genes (Types I and II) in the paraganglia system. This would require the improbable event of inactivation of all four alleles to trigger a paraganglioma.
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