title: Strict Regiospecificity of Human Epithelial 15-Lipoxygenase-2 Delineates Its Transcellular Synthesis Potential.
abstract: Lipoxins are an important class of lipid mediators that induce the resolution of inflammation and arise from transcellular exchange of arachidonic acid (AA)-derived lipoxygenase products. Human epithelial 15-lipoxygenase-2 (h15-LOX-2), the major lipoxygenase in macrophages, has exhibited strict regiospecificity, catalyzing only the hydroperoxidation of carbon 15 of AA. To determine the catalytic potential of h15-LOX-2 in transcellular synthesis events, we reacted it with the three lipoxygenase-derived monohydroperoxy-eicosatetraenoic acids (HPETE) in humans: 5-HPETE, 12-HPETE, and 15-HPETE. Only 5-HPETE was a substrate for h15-LOX-2, and the steady-state catalytic efficiency (kcat/Km) of this reaction was 31% of the kcat/Km of AA. The only major product of h15-LOX-2's reaction with 5-HPETE was the proposed lipoxin intermediate, 5,15-dihydroperoxy-eicosatetraenoic acid (5,15-diHPETE). However, h15-LOX-2 did not react further with 5,15-diHPETE to produce lipoxins. This result is consistent with the specificity of h15-LOX-2 despite the increased reactivity of 5,15-diHPETE. Density functional theory calculations determined that the radical, after abstracting the C10 hydrogen atom from 5,15-diHPETE, had an energy 5.4 kJ/mol lower than that of the same radical generated from AA, demonstrating the facility of 5,15-diHPETE to form lipoxins. Interestingly, h15-LOX-2 does react with 5S,6R-diHETE, forming LipoxinA4, indicating the gemdiol does not prohibit h15-LOX-2 reactivity. Taken together, these results demonstrate the strict regiospecificity of h15-LOX-2 that circumscribes its role in transcellular synthesis.
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Abigail R
authors.initials: AR
authors.lastname: Green
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Shannon
authors.initials: S
authors.lastname: Barbour
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Thomas
authors.initials: T
authors.lastname: Horn
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Jose
authors.initials: J
authors.lastname: Carlos
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Jevgenij A
authors.initials: JA
authors.lastname: Raskatov
authors.affiliation: Department Chemistry and Biochemistry, University of California at Santa Cruz , 1156 High Street, Santa Cruz, California 95064, United States.
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Holman
mesh_terms: D001093:Arachidonate 15-Lipoxygenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D006893:Hydroxyeicosatetraenoic Acids; C458528:ALOX15B protein, human; D001093:Arachidonate 15-Lipoxygenase