The urease-catalyzed hydrolysis of thiourea and thioacetamide

Archives of Biochemistry and Biophysics
C Lopreore, L D Byers

Abstract

Jack bean urease catalyzes the hydrolysis of thiourea with a second-order rate constant (kcat/Km) of 1.6 (+/- 0.2) x 10(-3) M-1 S-1 at pH7, 25 degrees C. This value is lower than that for urea by a factor of 3 x 10(8). The corresponding substitution of S for O in acetamide reduces the kcat/Km value by only a factor of 33. This greater reactivity of the oxo compounds than of the corresponding thiono compounds, and the tighter binding of urea (Ks = 2.9 mM) than of either the guanidinium ion (Ki = 30 mM) or thiourea (Ki = 70 mM), suggests that the substrate chalcogen (S or O) is more likely to be stabilized in the transition state by coordination to the enzyme via a neutral hydrogen-bond donor (i.e., Brønsted acid catalysis) than by coordination via one of the active-site nickel ions (i.e., Lewis acid catalysis).

Citations

Aug 15, 2012·Journal of Biological Inorganic Chemistry : JBIC : a Publication of the Society of Biological Inorganic Chemistry·Barbara KrajewskaMałgorzata Brindell
Sep 26, 2006·Applied and Environmental Microbiology·Anthony G DodgeLawrence P Wackett
Nov 23, 2012·Chemistry : a European Journal·Chang Woo KimYoung Soo Kang
Sep 25, 2007·Bioorganic & Medicinal Chemistry Letters·Kirubakaran SivapriyaSrinivasan Chandrasekaran
Apr 13, 2001·Inorganic Chemistry·A M Barrios, S J Lippard
Apr 29, 2004·Journal of the American Chemical Society·Xuefeng LuDebra Dunaway-Mariano

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