Enzymatic mechanisms for catalysis of enolization: ketosteroid isomerase
1Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, MD 21250, USA. pollack@umbc.edu
Abstract:
Breaking a carbon-hydrogen bond adjacent to a carbonyl is a slow step in a large number of chemical reactions. However, many enzymes are capable of catalyzing this reaction with great efficiency. One of the most proficient of these enzymes is 3-oxo-Delta5-steroid isomerase (KSI), which catalyzes the isomerization of a wide variety of 3-oxo-Delta5-steroids to their Delta4-conjugated isomers. In this review, the mechanism of KSI is discussed, with particular emphasis on energetic considerations. Both experimental and theoretical approaches are considered to explain the mechanistic details of the reaction.
Related Concept Videos
Reactivity of Enols
Regioselective Formation of Enolates
Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
Keto–Enol Tautomerism: Mechanism
Types of Enols and Enolates
Stereochemical Effects of Enolization


