Mitochondrial glutaryl-CoA dehydrogenase (GCDH) catalyzes the reaction of glutaryl-CoA and FAD to form crotonyl-CoA, FADH2, and CO2. The active enzyme is a tetramer of GCDH polypeptides lacking a 44-residue aminoterminal mitochondrial targeting sequence. Mutations in GCDH cause glutaric aciduria type 1 in vivo (Fu et al. 2004; Keyser et al. 2008).