title: Peroxidase active site activity assay.
abstract: Cyclooxygenase enzymes house spatially distinct cyclooxygenase- and peroxidase-active sites. The two-electron reduction of peroxides to their corresponding alcohols by the heme bound in the peroxidase-active site converts the heme to a ferryloxoprotoporyphrin cation radical, with a reductant providing the two electrons necessary to bring the heme back to its resting state. The ferryloxoprotoporyphrin cation radical can abstract a hydrogen atom from a tyrosine residue in the cyclooxygenase-active site, activating the oxygenase functionality. The tyrosyl radical subsequently abstracts a hydrogen atom from the cyclooxygenase substrate, arachidonic acid, leading to its oxygenation and the formation of a hydroperoxy endoperoxide intermediate, PGG(2). The peroxidase functionality reduces PGG(2) to the hydroxy endoperoxide, PGH(2), which serves as the precursor to downstream prostaglandins and thromboxane. The peroxidase activity of cycloxygenase enzymes can be assayed by quantifying the oxidation of a peroxidase reductant or the reduction of a hydroperoxide substrate. Here we describe a spectrophotometric assay used to measure the oxidation of a reductant, 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), as well as a high-performance liquid chromatography method for the measurement of the conversion of 5-phenyl-4-pentyl hydroperoxide (PPHP) to its corresponding alcohol. The first provides a continuous but indirect assay of peroxidase activity, whereas the second provides a discontinuous but direct assay.
authors.affiliation: A.B. Hancock Jr. Memorial Laboratory for Cancer Research, Department of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt University School of Medicine, Nashville, TN, USA.
authors.forename: Kelsey C
authors.initials: KC
authors.lastname: Duggan
authors.forename: Joel
authors.initials: J
authors.lastname: Musee
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Marnett
mesh_terms: D000475:Alkenes / Q000378:metabolism; D052160:Benzothiazoles; D020134:Catalytic Domain; D002851:Chromatography, High Pressure Liquid; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods; D013451:Sulfonic Acids / Q000378:metabolism; D013844:Thiazoles / Q000378:metabolism
chemical_list: D000475:Alkenes; D052160:Benzothiazoles; D013451:Sulfonic Acids; D013844:Thiazoles; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; C047254:5-phenylpent-4-enyl-1-hydroperoxide; D010544:Peroxidases; D011451:Prostaglandin-Endoperoxide Synthases