Optical spectra and kinetics of reactions of prostaglandin H synthase: Effects of the substrates 13-hydroperoxyoctadeca-9,11 -dienoic acid, arachidonic acid, N,N,N′,N′-tetramethyl- p-phenylenediamine, and phenol and of the nonsteroidal anti-inflammatory drugs aspirin, indomethacin, phenylbutazone, and Bromfenac

Abstract

A combination of cyclooxygenase activity assays, rapid spectrophotometry and presteady-state, steady-state, and transient-state kinetics is used to characterize further the properties of prostaglandin H synthase. 13-Hydroperoxyoctadeca-9-11-dienoic acid is used as oxidizing substrate and the effects of the following compounds are examined: arachidonic acid, N,N,N′,N′-tetramethyl- p-phenylenediamine, phenol, diethyldithiocarbamate, and the nonsteroidal anti-inflammatory drugs aspirin, indomethacin, phenylbutazone, and Bromfenac. The order of reactivity of four of these substrates, predominantly with compound II of prostaglandin H synthase, is N,N,N′,N′-tetramethyl- p-phenylenediamine > phenol > indomethacin ∼ phenylbutazone. Aspirin exhibits no effect. Arachidonic acid causes inactivation. Diethyldithiocarbamate acts as a reducing substrate for the oxidized forms of prostaglandin H synthase. Bromfenac appears to act both as a protective agent and inhibitor.