PHENYLALANINE-353 IS A PRIMARY DETERMINANT FOR THE POSITIONAL SPECIFICITY OF MAMMALIAN 15-LIPOXYGENASES

Mammalian lipoxygenases are implicated in the biosynthesis of inflamma tory mediators, ill the pathogenesis of atherosclerosis and in the pro cess of blood cell differentiation and maturation. With respect to the ir reaction specificity, three major types of mammalian lipoxygenases (15-lipoxygenases, 12-lipoxygenases and 5-lipoxygenases) may be classi fied. Although this nomenclature is commonly used, the mechanistic rea sons for the positional specificity of lipoxygenases are not well unde rstood. We investigated the structural reasons for lipoxygenase specif icity by a combination of chimera formation and site-directed mutagene sis, and identified phenylalanine 353 as primary determinant for the p ositional specificity of rabbit reticulocyte 15-lipoxygenase. Modeling of the enzyme-substrate interaction suggested that the alignment of a rachidonic acid at the active site appears to be influenced by this re sidue. According to the substrate orientation, the 15-lipoxygenase may be differentiated from two types of mammalian 12-lipoxygenases. (C) 1 996 Academic Press Limited