Literature summary for 2.2.1.6 extracted from

Chipman, D.; Barak, Z.; Shaanan, B.; Vyazmensky, M.; Binshtein, E.; Belenky, I.; Temam, V.; Steinmetz, A.; Golbik, R.; Tittmann, K.
Origin of the specificities of acetohydroxyacid synthases and glyoxylate carboligase (2009), J. Mol. Catal. B, 61, 50-55.

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Protein Variants

Protein Variants	Comment	Organism
V375A	mutation in isozyme AHAS II, allows 2-oxo-butanoate to be a good first substrate and the mutant enzyme can synthesize 2-propionyl-2-hydroxybutanoate	Escherichia coli

Organism

Organism	UniProt	Comment	Textmining
Escherichia coli	-	-	-

Substrates and Products (Substrate)

Substrates	Comment Substrates	Organism	Products	Comment (Products)	Rev.	Reac.
2-oxobutanoate + pyruvate	reaction catalyzed by mutant V375A	Escherichia coli	2-propionyl-2-hydroxybutanoate + ?	-	?
additional information	the specificity of AHAS for 2-ketoacids as acceptor substrates is due to an arginine residue which probably interacts with the carboxylate of the second substrate, e.g., Arg276 in AHAS II. Mutants altered at this arginine can utilize aromatic aldehydes as second substrate and form chiral arylacyl carbinols. Mechanistically, carboligation occurs after rate-determining formation of hydroxyethyl-thiamine diphosphate. A faster rate constant for product release when the alkyl group derived from the acceptor substrate is ethyl compared to methyl plays a major role in product specificity. The crucial role of a Trp residue, i.e. Trp 464 in AHAS II, in determining specificity may be due to control of a conformational change involved in product release rather than to affinity for 2-ketobutyrate	Escherichia coli	?	-	?
pyruvate	-	Escherichia coli	(S)-2-acetolactate + CO2	-	?

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Release 2023.1 (January 2023)