Kinetic study of the H103A mutant yeast transketolase.
FEBS Lett
; 567(2-3): 270-4, 2004 Jun 04.
Article
em En
| MEDLINE
| ID: mdl-15178335
ABSTRACT
Data from site-directed mutagenesis and X-ray crystallography show that His103 of holotransketolase (holoTK) does not come into contact with thiamin diphosphate (ThDP) but stabilizes the transketolase (TK) reaction intermediate, alpha,beta-dihydroxyethyl-thiamin diphosphate, by forming a hydrogen bond with the oxygen of its beta-hydroxyethyl group [Eur. J. Biochem. 233 (1995) 750; Proc. Natl. Acad. Sci. USA 99 (2002) 591]. We studied the influence of His103 mutation on ThDP-binding and enzymatic activity. It was found that mutation does not affect the affinity of the coenzyme to apotransketolase (apoTK) in the presence of Ca(2+) (a cation found in the native holoenzyme) but changes all the kinetic parameters of the ThDP-apoTK interaction in the presence of Mg(2+) (a cation commonly used in ThDP-dependent enzymes studies). It was concluded that the structures of TK active centers formed in the presence of Mg(2+) and Ca(2+) are not identical. Mutation of His103 led to a significant acceleration of the one-substrate reaction but a slow down of the two-substrate reaction so that the rates of both types of catalysis became equal. Our results provide evidence for the intermediate-stabilizing function of His103.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Saccharomyces cerevisiae
/
Transcetolase
Idioma:
En
Revista:
FEBS Lett
Ano de publicação:
2004
Tipo de documento:
Article
País de afiliação:
Federação Russa