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Catalysts 2014, 4(2), 174-185; doi:10.3390/catal4020174
Communication

Kinetic Isotope Effect of Prostaglandin H Synthase Exhibits Inverted Temperature Dependence

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Received: 28 February 2014 / Revised: 24 April 2014 / Accepted: 23 May 2014 / Published: 11 June 2014
(This article belongs to the Special Issue Enzymes in Organic Synthesis)
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Abstract

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.
Keywords: prostaglandin H synthase-1 and -2; deuterium kinetic isotope effect; temperature dependence of KIE prostaglandin H synthase-1 and -2; deuterium kinetic isotope effect; temperature dependence of KIE
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Wu, G.; Kulmacz, R.J.; Tsai, A.-L. Kinetic Isotope Effect of Prostaglandin H Synthase Exhibits Inverted Temperature Dependence. Catalysts 2014, 4, 174-185.

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