Remarkable Stabilization of Zwitterionic Intermediates May Account for a Billion-fold Rate Acceleration by Thiamin Diphosphate-Dependent Decarboxylases†
作者： Frank Jordan , Haijuan Li , Angela Brown
DOI: 10.1021/BI990373G
关键词: Kinetics 、 Enzyme 、 Cofactor 、 Acid dissociation constant 、 Chemistry 、 Pyruvate decarboxylase 、 Dissociation (chemistry) 、 Enamine 、 Stereochemistry 、 Active center
摘要: When the E91D variant of apo-yeast pyruvate decarboxylase (EC 4.1.1. 1) is exposed to C2alpha-hydroxybenzylthiamin diphosphate, this putative intermediate partitioned on enzyme between release benzaldehyde product (as evidenced by regeneration active enzyme) and dissociation proton at C2alpha form enamine-C2alpha-carbanion intermediate. While pKa (the negative log acid constant) for approximately 15.4 in water, formation enamine pH 6.0 indicates a >9 unit suppression environment. The dramatic stabilization zwitterionic center sufficient account as much 10(9)-fold rate acceleration enzyme. This "solvent" effect could be useful achieving bulk provided protein over above that afforded coenzyme all thiamin diphosphate-dependent 2-oxo decarboxylases.
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