Lipoxygenases are a family of iron-containing enzymes that catalyse the dioxygenation of polyunsaturated fatty acids in lipids containing a cis,cis-1,4- pentadiene structure. It catalyses the following reaction:
Lipoxygenases are found in plants, animals and fungi. Products of lipoxygenases are involved in diverse cell functions.
The two long central helices cross at the active site; both helices include internal stretches of π-helix that provide three histidine (His) ligands to the active site iron. Two cavities in the major domain of soybean lipoxygenase-1 (cavities I and II) extend from the surface to the active site. The funnel-shaped cavity I may function as a dioxygen channel; the long narrow cavity II is presumably a substrate pocket. The more compact mammalian enzyme contains only one boot-shaped cavity (cavity II). In soybean lipoxygenase-3 there is a third cavity which runs from the iron site to the interface of the β-barrel and catalytic domains. Cavity III, the iron site and cavity II form a continuous passage throughout the protein molecule.
The active site iron is coordinated by Nε of three conserved His residues and one oxygen of the C-terminal carboxyl group. In addition, in soybean enzymes the side chain oxygen of asparagine is weakly associated with the iron. In rabbit lipoxygenase, this Asn residue is replaced with His which coordinates the iron via Nδ atom. Thus, the coordination number of iron is either five or six, with a hydroxyl or water ligand to a hexacoordinate iron.
|lipoxygenase||(linoleate:oxygen 13-oxidoreductase)||linoleate + O2 = (9Z,11E,13S)-13-hydroperoxyoctadeca-9,11-dienoate|
|arachidonate 12-lipoxygenase||(arachidonate:oxygen 12-oxidoreductase)||arachidonate + O2 = (5Z,8Z,10E,12S,14Z)-12-hydroperoxyicosa-5,8,10,14-tetraenoate|
|arachidonate 15-lipoxygenase||(arachidonate:oxygen 15-oxidoreductase)||arachidonate + O2 = (5Z,8Z,11Z,13E,15S)-15-hydroperoxyicosa-5,8,11,13-tetraenoate|
|arachidonate 5-lipoxygenase||(arachidonate:oxygen 5-oxidoreductase)||arachidonate + O2 = leukotriene A4 + H2|
|arachidonate 8-lipoxygenase||(arachidonate:oxygen 8-oxidoreductase)||arachidonate + O2 = (5Z,8R,9E,11Z,14Z)-8-hydroperoxyicosa-5,9,11,14-tetraenoate|
Soybean Lipoxygenase 1 exhibits the largest H/D kinetic isotope effect (KIE) on kcat (kH/kD) (81 near room temperature) so far reported for a biological system.
Association of a lipoxygenase locus, Lpx-B1, with variation in lipoxygenase activity in durum wheat seeds. (Cell Biology & Molecular Genetics).(Statistical Data Included)
Sep 01, 2002; WHEAT IS USED to make breads, pasta, beer, pastries and cereals. Because of its long shelf life, wheat grain can be stored for...