Kinetic Isotope Effect of Prostaglandin H Synthase Exhibits Inverted Temperature Dependence

• Main Authors: Gang Wu, Richard J. Kulmacz, Ah-Lim Tsai
• Format: Article
• Language: English
• Published: MDPI AG 2014-06-01
• Series: Catalysts
• Subjects: prostaglandin H synthase-1 and -2; deuterium kinetic isotope effect; temperature dependence of KIE
• Online Access: http://www.mdpi.com/2073-4344/4/2/174

Conversion of arachidonic acid to prostaglandin G2/H2 catalyzed by prostaglandin H synthase (PGHS) is proposed to involve initial transfer of the C13 pro-(S) hydrogen atom from arachidonate to the Tyr385 radical in PGHS, followed by insertion of two oxygen molecules and several chemical bond rearrangements. The initial hydrogen-transfer was recently concluded to be a rate-limiting step in cyclooxygenase catalysis based on the observed intrinsic deuterium kinetic isotope effect values (Dkcat). In the present study, we have found that Dkcat values of both PGHS-1 and -2 show an unusual increase with temperatures in the range of 288–310 K, exhibiting an inverted temperature dependence. The value of lnDkcat, however, decreased linearly with 1/T, consistent with a typical Arrhenius relationship.