<p>In <taxon tax_id="562">Escherichia coli</taxon> and many other bacteria, two small, hydrophobic, mutually homologous subunits of succinate dehydrogenase (a TCA cycle enzyme) are SdhC and SdhD. This entry is the SdhD, the hydrophobic membrane anchor protein. SdhC is apocytochrome b558, which also plays a role in anchoring the complex.</p>