Spectral properties of the higher oxidation states of prostaglandin H synthase

Abstract

Prostaglandin H (PGH) synthase reacts with organic hydroperoxides and fatty acid hydroperoxides on a millisecond time scale to generate an intermediate that is spectrally similar to compound I of horseradish peroxidase. Compound I of PGH synthase is converted to compound II within 170 ms. Compound II decays to resting enzyme in a few seconds. Thus, the peroxidase reaction of PGH synthase appears to involve a cycle of native enzyme, compound I, and compound II, typical of heme-containing peroxidases. The Soret absorption maximum of compound I appears to occur at 412 nm but a small amount of compound II may be present. Soret maxima occur at 420, 433, and 419 for compound II, the ferrous enzyme, and the oxyferrous enzyme (compound III), respectively. Rapid scan analysis of the reaction of PGH synthase with arachidonic acid reveals the absorbance of compound II but no evidence for ferrous or oxyferrous enzyme.