Before forming a heterodimer with subunit SDHB, some portion of SDHA with covalently bound FAD appears to interact with other assembly factor – SDHAF4 (Sdh8 in yeast). Unbound flavinylated SDHA dimerizes with SDHAF4 which serves as a chaperone. Studies suggest that formation of SDHA-SDHB dimer is impaired in absence of SDHAF4 so the chaperon-like assembly factor might facilitate interaction of the subunits. Moreover, SDHAF4 seems to prevent ROS generation via accepting electrons from succinate which can be still oxidized by unbound monomeric SDHA subunit.