Effects of Native and Permethylated Cyclodextrins on the Catalytic Activity of L-Tryptophan indole lyase
ABSTRACT The impact of native and permethylated α-, β-, and γ-cyclodextrins on the L-tryptophan indole lyase-catalyzed decomposition of L-tryptophan was investigated by means of spectrophotometric measurements. The inhibitory effects of cyclodextrins on the catalytic
activity of the enzyme are shown. The observed inhibition is of mixed type, i.e. competitive and non-competitive. This phenomenon
is supposed to be the result of host–guest complex formation involving cyclodextrins and L-tryptophan, and probably between aromatic amino acid residues on the surface of the investigated enzyme. Therefore cyclodextrins
were found to have an impact on the maximal velocity and on the Michaelis constant of the described catalysis. The competitive
inhibition does not only depend on the stabilities of inclusion complexes, but mainly on their structures.
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ABSTRACT: Cyclomaltohexaose (α-cyclodextrin) and cyclomaltoheptaose (β-cyclodextrin) as well as their four methyl ether derivatives, that is, hexakis(2,3-di-O-methyl)cyclomaltohexaose, hexakis(2,3,6-tri-O-methyl)cyclomaltohexaose, heptakis(2,3-di-O-methyl)cyclomaltoheptaose, and heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose were investigated as the additives in the course of enzymatic decomposition of l-phenylalanine catalyzed by phenylalanine ammonia-lyase. Only a few of those additives behaved like classical inhibitors of the enzymatic reaction under investigation because the values of the Michaelis constants that were obtained, as well as the maximum velocity values depended mostly atypically on the concentrations of those additives. In most cases cyclodextrins caused mixed inhibition, both competitive and noncompetitive, but they also acted as activators for selected concentrations. This atypical behaviour of cyclodextrins is caused by three different and independent effects. The inhibitory effect of cyclodextrins is connected with the decrease of substrate concentration and unfavourable influence on the flexibility of the enzyme molecules. On the other hand, the activating effect is connected with the decrease of product concentration (the product is an inhibitor of the enzymatic reaction under investigation). All these effects are caused by the ability of the cyclodextrins to form inclusion complexes.Carbohydrate research 06/2011; 346(13):1855-9. · 2.03 Impact Factor