Membrane-anchoring subunit of succinate dehydrogenase (SDH) that is involved in complex II of the mitochondrial electron transport chain and is responsible for transferring electrons from succinate to ubiquinone (coenzyme Q) (PubMed:10482792, PubMed:9533030). SDH also oxidizes malate to the non-canonical enol form of oxaloacetate, enol- oxaloacetate (By similarity). Enol-oxaloacetate, which is a potent inhibitor of the succinate dehydrogenase activity, is further isomerized into keto-oxaloacetate (By similarity). {ECO:0000250|UniProtKB:Q95123, ECO:0000269|PubMed:10482792, ECO:0000269|PubMed:9533030}. This is the function of Ensembl gene identifier ENSG00000204370 (SDHD, succinate dehydrogenase complex subunit D).