Iron-sulfur protein (IP) 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). a quinone + succinate = a quinol + fumarate Binds 1 [2Fe-2S] cluster. Binds 1 [3Fe-4S] cluster. Binds 1 [4Fe-4S] cluster. Carbohydrate metabolism; tricarboxylic acid cycle; fumarate from succinate (eukaryal route): step 1/1. Component of complex II composed of four subunits: a flavoprotein (FP), an iron-sulfur protein (IP), and a cytochrome b composed of a large and a small subunit. Belongs to the succinate dehydrogenase/fumarate reductase iron-sulfur protein family.