<p>8-amino-7-oxononanoate synthase (AONS) is a pyridoxal 5'-phosphate-dependent enzyme, which catalyses the decarboxylative condensation of L-alanine with pimeloyl-CoA to form 8(S)-amino-7-oxononanoate. This is the first committed step in biotin biosynthesis [<cite idref="PUB00024209"/>]: <reaction>6-carboxyhexanoyl-CoA + L-alanine = 8-amino-7-oxononanoate + CoA + CO2</reaction> </p><p>The enzyme is a symmetrical homodimer with a tertiary structure and active site organisation similar to, but distinct from, those of other PLP-dependent enzymes with known structures. AONS is a critical PLP-binding lysine at the end of a deep cleft that allows access to the pantothenate arm of pimeloyl-CoA. There is a cluster of positively charged residues at the entrance to this cleft, which forms a putative diphosphate binding site for CoA [<cite idref="PUB00023713"/>]. Trifluoroalanine irreversibly inhibits this enzyme [<cite idref="PUB00040947"/>].</p> 8-amino-7-oxononanoate synthase/2-amino-3-ketobutyrate coenzyme A ligase