title: Reactions of prostaglandin H synthase in the presence of the stabilizing agents diethyldithiocarbamate and glycerol.
abstract: Both cyclooxygenase and peroxidase reactions of prostaglandin H synthase were studied in the presence and absence of diethyldithiocarbamate and glycerol at 4 degrees C in phosphate buffer (pH 8.0). Diethyldithiocarbamate reacts with the high oxidation state intermediates of prostaglandin H synthase; it protects the enzyme from bleaching and loss of activity by its ability to act as a reducing agent. For the reaction of diethyldithiocarbamate with compound I, the second-order rate constant k2,app, was found to fall within the range of 5.8 x 10(6) +/- 0.4 x 10(6) M-1.s-1 less than k2,app less than 1.8 x 10(7) +/- 0.1 x 10(7) M-1.s-1. The reaction of diethyldithiocarbamate with compound II showed saturation behavior suggesting enzyme-substrate complex formation, with kcat = 22 +/- 3 s-1, Km = 67 +/- 10 microM, and the second-order rate constant k3,app = 2.0 x 10(5) +/- 0.2 x 10(5) M-1.s-1. In the presence of both diethyldithiocarbamate and 30% glycerol, the parameters for compound II are kcat = 8.8 +/- 0.5 s-1, Km = 49 +/- 7 microM, and k3,app = 1.03 x 10(5) +/- 0.07 x 10(5) M-1.s-1. The spontaneous decay rate constants of compounds I and II (in the absence of diethyldithiocarbamate) are 83 +/- 5 and 0.52 +/- 0.05 s-1, respectively, in the absence of glycerol; in the presence of 30% glycerol they are 78 +/- 5 and 0.33 +/- 0.02 s-1, respectively. Neither cyclooxygenase activity nor the rate constant for compound I formation using 5-phenyl-4-pentenyl-1-hydroperoxide is altered by the presence of diethyldithiocarbamate.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Hsuanyu
authors.forename: H B
authors.initials: HB
authors.lastname: Dunford
mesh_terms: D000818:Animals; D004050:Ditiocarb; D004795:Enzyme Stability; D005990:Glycerol; D007700:Kinetics; D008297:Male; D008958:Models, Molecular; D009195:Peroxidase; D011451:Prostaglandin-Endoperoxide Synthases / Q000302:isolation & purification / Q000378:metabolism*; D012669:Seminal Vesicles / Q000201:enzymology; D012756:Sheep
chemical_list: D004050:Ditiocarb; D009195:Peroxidase; D011451:Prostaglandin-Endoperoxide Synthases; D005990:Glycerol