Complex II in mitochondria, of which succinate dehydrogenase (EC 1.3.99.1) is a component, has 4 subunits. In order of decreasing molecular mass, they are the flavoprotein (SDHA), the iron sulfur protein (SDHB), and the 2 integral membrane proteins, SDHC and SDHD.

Kita et al. (1990) cloned and sequenced the iron sulfur protein subunit. A clone was isolated from a human liver cDNA library. The open reading frame encodes a 252-amino acid protein. The amino acid sequence showed approximately 94% homology with that of bovine heart. Au et al. (1995) described the complete genomic clone for the gene encoding the iron sulfur protein subunit.