Antibody-Catalyzed Benzoin Oxidation as a Mechanistic Probe for Nucleophilic Catalysis by an Active Site Lysine
| Autor: | Ehud Keinan, Rachel Oizerowich, Hagit Shulman, Genia Sklute |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
Reaction mechanism
Schiff base Molecular Structure biology Stereochemistry Lysine Organic Chemistry Active site Antibodies Catalytic General Chemistry Catalysis Enamine Immunoglobulin Fab Fragments chemistry.chemical_compound Benzoin chemistry Aldol reaction Nucleophile Fructose-Bisphosphate Aldolase biology.protein Organic chemistry Aldol condensation Oxidation-Reduction |
| Zdroj: | Chemistry - A European Journal. 10:2159-2165 |
| ISSN: | 1521-3765 0947-6539 |
| DOI: | 10.1002/chem.200305034 |
| Popis: | + ) Incumbent of the Benno Gitter & Ilana Ben-Ami chair of Biotech- nology, Technion. Abstract: Aldolase antibody 24H6, which was obtained by reactive immu- nization against a 1,3-diketone hapten, is shown to catalyze additional reac- tions, including H/D exchange and oxi- dation reactions.Comparison of the H/D exchange reaction at the a-posi- tion of a wide range of aldehydes and ketones by 24H6 and by other aldolase antibodies, such as 38C2, pointed at the significantly larger size of the 24H6 active site.This property allowed for the catalysis of the oxidation of substi- tuted benzoins to benzils by potassium ferricyanide.This reaction was used as a mechanistic probe to learn about the initial steps of the 24H6-catalyzed aldol condensation reaction.The Hammett correlation (1 = 4.7) of log(kcat) versus the substituent constant, s, revealed that the reaction involves rapid forma- tion of a Schiff base intermediate from the ketone and an active site lysine res- idue.The rate-limiting step in this oxi- dation reaction is the conversion of the Schiff base to an enamine intermediate. In addition, linear correlation (1 = 3.13) was found between log(KM) and s, indicating that electronic rather than steric factors are dominant in the anti- body±substrate binding phenomenon and confirming that the reversible for- mation of a Schiff base intermediate comprises part of the substrate-binding mechanism. |
| Databáze: | OpenAIRE |
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