Aliphatic amidases catalyze the hydrolysis of short-chain aliphatic amides to form ammonia and the corresponding organic acid. This group includes Pseudomonas aeruginosa (Pa) AmiE, the amidase from Geobacillus pallidus RAPc8 (RAPc8 amidase), and Helicobacter pylori (Hp) AmiE and AmiF. PaAimE and HpAmiE hydrolyze various very short aliphatic amides, including propionamide, acetamide and acrylamide. HpAmiF is a formamidase which specifically hydrolyzes formamide. These proteins belong to a larger nitrilase superfamily comprised of nitrile- or amide-hydrolyzing enzymes and amide-condensing enzymes, which depend on a Glu-Lys-Cys catalytic triad. This superfamily has been classified in the literature based on global and structure based sequence analysis into thirteen different enzyme classes (referred to as 1-13), this subgroup corresponds to class 2. Members of this superfamily generally form homomeric complexes, the basic building block of which is a homodimer. HpAmiE , HpAmiF, and RAPc8 amidase, and PaAimE appear to be homohexameric enzymes, trimer of dimers.