Secondary .beta.-deuterium isotope effects in decarboxylation and elimination reactions of .alpha.-lactylthiamin: intrinsic isotope effects of pyruvate decarboxylase.

摘要: The reactions of the adduct pyruvate and thiamine, lactylthiamin (2-(lact-2-yl)thiamine), are accurate nonenzymic models for intermediates formed during catalysis by decarboxylase. enzymatic reaction generates diphosphate from thiamine diphosphate. ..beta..-Deuterium isotope effects were determined reactions, results related to on enzymic reaction. 2-(Lact-2-yl-..beta..-d/sub 3/) was prepared condensation methyl pyruvate-d/sub 3/ with followed hydrolysis. effect decarboxylation in acidic solution at 25/sup 0/C (k/sub H3//k/sub D3/) is 1.09 (standard deviation (SD) 0.015) pH 3.8, 0.5 M sodium acetate: = 1.095 (SD 0.014) 0.001 HCl. also studied using 38% ethanolic aqueous acetate (pH 3.8 before mixing ethanol) since sites less polar than water significantly accelerated cosolvent. within statistical range that water, 1.105 0.016), indicating acceleration solvent does not change extent hyperconjugative stabilization transition state relative ground state. base-catalyzed elimination determinedmore » kinetic studies multiwavelength analysis 11 carbonate solution. 1.12 0.01), which slightly higher decarboxylation.« less