Enhanced enzymatic activity of phenylalanine dehydrogenase caused by cyclodextrins

• Cyclodextrins (CDs) improve significantly the enzyme kinetics parameters.
• CDs tune l-phenylalanine (Phe) and phenylpyruvate (PP) biotransformations.
• This is due to different structures of the Phe–CD and PP–CD complexes.
• Our findings could help improve the synthesis and detection of Phe.

The influence of cyclodextrins (CDs) on the biotransformations of l-phenylalanine (Phe) and phenylpyruvate (PP) catalysed by phenylalanine dehydrogenase (PheDH) was evaluated. It was found that the reaction rate of both transformations was increased more than twice by CDs. The observed increase of the enzymatic activity is connected with the beneficial influence of CDs on the active conformation of PheDH due to formation of inclusion complexes on the surface of the enzyme protein. Moreover, the formation of the Phe–CD and PP–CD complexes was also postulated and studied theoretically by semiempirical calculations. The specificity of PheDH for Phe–CD increased over 6-fold in comparison with that for free Phe molecules. On the other hand, the specificity of PheDH for PP–CD decreased three times as compared with that for uncomplexed PP molecules. These reversed specificities of PheDH for complexed and free substrate molecules seem to be related to different properties of the Phe–CD and PP–CD inclusion complexes. Nevertheless, those CD complexes could not be considered as straight substrates for PheDH, the CDs rather play a role of transporting molecules with different abilities for donating free Phe or PP to the active site of the enzyme.

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