Mitochondrial ethylglutaconyl-CoA hydratase (AUH) catalyzes the hydrolysis of beta-methylglutaconyl-CoA to yield beta-hydroxy-beta-methylglutaryl-CoA (IJlst et al. 2002; Narisawa et al. 1986). Crystallographic studies have shown the active enzyme to be a hexamer of AUH polypeptides whose aminoterminal 67 residues, a mitochondrial targeting sequence, have been removed ((Kurimoto et al. 2001).