Effects of Native and Permethylated Cyclodextrins on the Catalytic Activity of L-Tryptophan indole lyase

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.