Lipoxygenase: a molecular complex with a non-heme iron

Abstract

Lipoxygenases are enzymes involved in the metabolism of polyunsaturated fatty acids. One molecule of the complex lipoxygenase-3 (L3) contains one atom of iron per enzyme (approx, 95 kDa). The iron cofactor is neither coordinated by porphyrins (heme moiety, as in hemoglobin), nor surrounded by a cluster of sulfur atoms. The enzyme could be described as an elaborate coordination complex that serves as a catalyst in a typical redox process involving an iron cation wrapped in its “host” enzyme, molecular oxygen, and a substrate that undergoes peroxygenation to an organic peroxide. The structure of soybean lipoxygenase L3 has been solved and refined to a discrepancy factor R = 23%, for 2.6 Å resolution data and 805 residues out of 857. The iron cation is buried inside the protein molecule. The active site shows three oxygen atoms and three nigrogen atoms as possible iron ligands in a pseudo- C 3v configuration, with nitrogen atoms grouped together at one side and oxygen atoms gathered at the opposite end of the pseudo-3-fold axis.