LIPOXYGENASE - A MOLECULAR-COMPLEX WITH A NONHEME IRON

Lipoxygenases are enzymes involved in the metabolism of polyunsaturate d fatty acids. One molecule of the complex lipoxygenase-3 (L3) contain s one atom of iron per enzyme (approx. 95 kDa). The iron cofactor is n either 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 t ypical redox process involving an iron cation wrapped in its ''host'' enzyme, molecular oxygen, and a substrate that undergoes peroxygenatio n to an organic peroxide. The structure of soybean lipoxygenase L3 has been solved and refined to a discrepancy factor R = 23%, for 2.6 Angs trom resolution data and 805 residues out of 857. The iron cation is b uried inside the protein molecule. The active site shows three oxygen atoms and three nitrogen 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.