Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine.

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Research Abstract Details 

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Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Abstract Text:

Krisztina Toth,John P Richard,

First-order rate constants for deprotonation of the alpha-imino carbon of the adduct between 5'-deoxypyridoxal (1) and glycine were determined as the rate constants for Claisen-type addition of glycine to 1 where deprotonation is rate determining for product formation. There is no significant deprotonation at pH 7.1 of the form of the 1-glycine iminium ion with the pyridine nitrogen in the basic form. The value of kHO for hydroxide ion-catalyzed deprotonation of the alpha-imino carbon increases from 7.5 x 10(2) to 3.8 x 10(5) to 3.0 x 10(7) M(-1) s(-1), respectively, with protonation of the pyridine nitrogen, the phenoxide oxyanion, and the carboxylate anion of the 1-glycine iminium ion. There is a corresponding decrease in the pKas for deprotonation of the alpha-imino carbon from 17 to 11 to 6. It is proposed that enzymes selectively bind and catalyze the reaction of the iminium ion with pKa = 17. A comparison of kB = 1.7 x 10(-3) s(-1) for deprotonation of the alpha-imino carbon of this cofactor-glycine adduct (pKa = 17 by HPO4(2-) with k(cat)/K(m) = 4 x 10(5) M(-1) s(-1) for catalysis of amino-acid racemization by alanine racemase shows that the enzyme causes a ca 2 x 10(8)-fold acceleration of the rate of deprotonation the alpha-imino carbon. This corresponds to about one-half of the burden borne by alanine racemase in catalysis of deprotonation of alanine.

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Publishing Authors By Initials

K Toth,JP Richard,

For similar heterocyclic compounds: heterocyclic compounds, 1-ring: pyridines: picolines: vitamin b 6: pyridoxal research abstracts see: heterocyclic compounds: heterocyclic compounds, 1-ring: pyridines: picolines: vitamin b 6: pyridoxal research

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Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Journal Published:

PUBLICATION TYPE: Research Support, N.I.H., Extr

Journal: Journal of the American Chemical Society

VOLUME: 129

Page Numbers: 3013-21

Journal Abbreviation: J. Am. Chem. Soc.

ISSN: 0002-7863

DAY: 14

MONTH: 02

YEAR: 2007

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Information

Number of References:

LANGUAGE: eng

NlmUniqueID: 7503056

Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Keywords Mesh Terms:

KEYWORDS: Pyridoxal

MESH TERMS: chemistry

Chemical & Substance for Abstract: Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine. Information

Substance Name: Alanine Racemase

Registry Number: EC 5.1.1.1

Grant and Affiliation Information for Covalent catalysis by pyridoxal: evaluation of the effect of the cofactor on the carbon acidity of glycine.

AFFILIATION: Department of Chemistry, University at Buffalo, SUNY, Buffalo, New York 14260, USA.

Country: United States

AGENCY: United States NIGMS

GRANT: GM 39754

ACRONYM: GM

MEDLINETA: J Am Chem Soc

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