Do Electrostatic Interactions with Positively Charged Active Site Groups Tighten the Transition State for Enzymatic Phosphoryl Transfer?
摘要:
The effect of electrostatic interactions on the transition-state character for enzymatic phosphoryl transfer has been a subject of much debate. In this work, we investigate the transition state for alkaline phosphatase (AP) using linear free-energy relationships (LIFERs). We determined k(cat)/K-M for a series of aryl sulfate ester monoanions to obtain the Bronsted coefficient, beta(lg)., and compared the value to that obtained previously for a series of aryl phosphorothioate ester dianion substrates. Despite the difference in substrate charge, the observed Bronsted coefficients for AP-catalyzed aryl sulfate and aryl phosphorothioate hydrolysis (-0.76 +/- 0.14 and -0.77 +/- 0.10, respectively) are strikingly similar, with steric effects being responsible for the uncertainties in these values. Aryl sulfates and aryl phosphates react via similar loose transition states in solution. These observations suggest an apparent equivalency of the transition states for phosphorothioate and sulfate hydrolysis reactions at the AP active site and, thus, negligible effects of active site electrostatic interactions on charge distribution in the transition state.
Sulfonation and sulfation in the reactions of the chloro- and dichlorophenols, 3-fluorophenol and (2,3-, 2,4- and 3,4-dichlorophenoxy)acetic acid with concentrated aqueous sulfuric acid and sulfur trioxide
作者:Peter de Wit、Hans Cerfontain
DOI:10.1002/recl.19881070303
日期:——
The chloro- and dichlorophenols have been sulfonated with sulfuric acid and with SO3 in aprotic solvents. In the sulfonations with concentrated aqueous sulfuric acid, the sulfonic acid isomer distribution is determined mainly by the ortho- and para-directing and activating effect of the hydroxy substituent; this is also the determining factor in the aprotic sulfonations using up to 1.0 equiv of SO3
Do Electrostatic Interactions with Positively Charged Active Site Groups Tighten the Transition State for Enzymatic Phosphoryl Transfer?
作者:Ivana Nikolic-Hughes、Douglas C. Rees、Daniel Herschlag
DOI:10.1021/ja0480421
日期:2004.9.1
The effect of electrostatic interactions on the transition-state character for enzymatic phosphoryl transfer has been a subject of much debate. In this work, we investigate the transition state for alkaline phosphatase (AP) using linear free-energy relationships (LIFERs). We determined k(cat)/K-M for a series of aryl sulfate ester monoanions to obtain the Bronsted coefficient, beta(lg)., and compared the value to that obtained previously for a series of aryl phosphorothioate ester dianion substrates. Despite the difference in substrate charge, the observed Bronsted coefficients for AP-catalyzed aryl sulfate and aryl phosphorothioate hydrolysis (-0.76 +/- 0.14 and -0.77 +/- 0.10, respectively) are strikingly similar, with steric effects being responsible for the uncertainties in these values. Aryl sulfates and aryl phosphates react via similar loose transition states in solution. These observations suggest an apparent equivalency of the transition states for phosphorothioate and sulfate hydrolysis reactions at the AP active site and, thus, negligible effects of active site electrostatic interactions on charge distribution in the transition state.