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

Journal Article · Wed Nov 26 04:00:00 EST 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00284a056· OSTI ID:6952264

Kluger, R; Brandl, M

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

• Research Organization: Univ. of Toronto, Ontario
• OSTI ID: 6952264
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:24; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ADDUCTS
AMINES
AZINES
AZOLES
CARBOXYLIC ACIDS
CATALYSIS
CHEMICAL REACTION KINETICS
DATA
DEUTERIUM
DEUTERIUM COMPOUNDS
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXY COMPOUNDS
INFORMATION
ISOTOPE EFFECTS
ISOTOPES
KETO ACIDS
KINETICS
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PYRIMIDINES
PYRUVIC ACID
REACTION INTERMEDIATES
REACTION KINETICS
STABLE ISOTOPES
THIAMINE
THIAZOLES
VITAMIN B GROUP
VITAMINS