Oxidation kinetics of caffeic acid by prostaglandin H synthase: potential role in regulation of prostaglandin biosynthesis.
The naturally occurring catechol derivative caffeic acid is a moderate stimulator of prostaglandin H synthase cyclooxygenase activity and a good reducing substrate for prostaglandin H synthase-compounds I and II. The discrepancy between the two properties is explained by a specific peroxidative mechanism that includes the formation of an inhibitory complex of caffeic acid with native enzyme followed by a three-step irreversible ping-pong peroxidation. The concentration of caffeic acid necessary to produce 50% stimulation of 0.2 mM arachidonic acid oxidation is 0.8 +/- 0.1 mM. The rate constant for the reaction of prostaglandin H synthase with hydrogen peroxide, determined from steady-state results, is (5.68 +/- 0.1) x 10(5) M-1 s-1. The rate constant for the reaction of prostaglandin H synthase-compound II with caffeic acid is (1.25 +/- 0.1) x 10(6) M-1 s-1. The dissociation constant of caffeic acid from the inhibitory complex is 35 +/- 10 microM. In diluted enzyme solutions, caffeic acid binding is diminished and the enzyme exhibits higher peroxidase activity. Our results suggest that caffeic acid is not a O-demethylation product of ferulic acid degradation catalyzed by prostaglandin H synthase, nor a chelating agent for the heme iron. The oxidation of caffeic acid could be important in the regulation of both prostaglandin H synthase and lipoxygenase activities and hence prostaglandin and leukotriene biosynthesis.
Bakovic
M
M
Department of Chemistry, University of Alberta, Edmonton, Canada.
Dunford
H B
HB
D016718:Arachidonic Acid / Q000378:metabolism; D002109:Caffeic Acids / Q000378:metabolism* / Q000494:pharmacology; D003373:Coumaric Acids / Q000378:metabolism / Q000494:pharmacology; D006735:Horseradish Peroxidase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011453:Prostaglandins / Q000096:biosynthesis*
D002109:Caffeic Acids; D003373:Coumaric Acids; D011453:Prostaglandins; D016718:Arachidonic Acid; C004999:ferulic acid; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D011451:Prostaglandin-Endoperoxide Synthases; C040048:caffeic acid