Succinate dehydrogenase [ubiquinone] iron-sulfur subunit, mitochondrial (SDHB) also known as iron-sulfur subunit of complex II (Ip) is a protein that in humans is encoded by the SDHB gene. The succinate dehydrogenase (also called SDH or Complex II) protein complex catalyzes the oxidation of succinate (succinate + ubiquinone => fumarate + ubiquinol). SDHB is one of four protein subunits forming succinate dehydrogenase, the other three being SDHA, SDHC and SDHD. The SDHB subunit is connected to the SDHA subunit on the hydrophilic, catalytic end of the SDH complex. It is also connected to the SDHC/SDHD subunits on the hydrophobic end of the complex anchored in the mitochondrial membrane. The subunit is an iron-sulfur protein with three iron-sulfur clusters. It weighs 30 kDa.