Acyl-Acyl Carrier Protein Desaturase (Acyl_ACP_Desat) is a mu-oxo-bridged diiron-carboxylate enzyme, which belongs to a broad superfamily of ferritin-like proteins and catalyzes the NADPH and O2-dependent formation of a cis-double bond in acyl-ACPs. Acyl-ACP desaturases are found in higher plants and a few bacterial species (Mycobacterium tuberculosis, M. leprae, M. avium and Streptomyces avermitilis, S. coelicolor). In plants, Acyl-ACP desaturase is a plastid-localized, covalently ACP linked, soluble desaturase that introduces the first double bound into saturated fatty acids, resulting in the corresponding monounsaturated fatty acid. Members of this class of soluble desaturases are specific for a particular substrate chain length and introduce the double bond between specific carbon atoms. For example, delta 9 stearoyl-ACP is specific for stearic acid and introduces a double bond between carbon 9 and 10 to yield oleic acid in the ACP-bound form. The enzymatic reaction requires molecular oxygen, NAD(P)H, NAD(P)H ferredoxin oxido-reductase and ferredoxin. The enzyme is active in the homodimeric form; the monomer consists mainly of alpha-helices with the catalytic diiron center buried within a four-helix bundle. Integral membrane fatty acid desaturases that introduce double bonds into fatty acid chains, acyl-CoA desaturases of animals, yeasts, and fungi, and acyl-lipid desaturases of cyanobacteria and higher plants, are distinct from soluble acyl-ACP desaturases, lack diiron centers, and are not included in this CD.
Structure:1OQ9; Ricinus communis (castor bean) Stearoyl-ACP desaturase complexed with acetate. - View structure with Cn3D
Comment:The stearoyl-ACP desaturase - acetate complex is proposed to mimic a stable mu-1,2-peroxo intermediate closely related to the catalytically competent species present during productive turnover.