PMID: 2511429Nov 1, 1989Paper

Mechanism of inhibition of prostaglandin H synthase by eugenol and other phenolic peroxidase substrates

Molecular Pharmacology
D C Thompson, T E Eling

Abstract

The mechanism of inhibition of prostaglandin H synthase (PHS) by eugenol was investigated using purified apoenzyme reconstituted with either manganese protoporphyrin IX (Mn-PHS) or hematin (Fe-PHS). Eugenol stimulated Fe-PHS activity at low concentrations and inhibited at higher concentrations, an activity typical of many phenolic compounds. Eugenol was also an excellent reducing cosubstrate for the peroxidase, being cooxidized to a reactive quinone methide in the process. Higher concentrations of eugenol were required to inhibit Fe-PHS than Mn-PHS (which retains cyclooxygenase activity but not peroxidase activity). Inhibition by eugenol was highly dependent on arachidonic acid concentration. In experiments using Mn-PHS, eugenol increased the time required for the initiation of O2 consumption after addition of arachidonic acid and also inhibited the rate of O2 uptake. Eugenol did not, however, affect the total amount of O2 consumed. The addition of 10 microM hydroperoxide (prostaglandin G2) to these incubations did not prevent the inhibitory effects of eugenol. Other phenolic compounds, including guaiacol, butylated hydroxyanisole, and acetaminophen inhibited Mn-PHS in a manner similar to eugenol. These results demonstrate that...Continue Reading

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