Loss of Bacillus Badius Phenylalanine Dehydrogenase Specificity towards Phenylalanine Substrate in Presence of CdTe Quantum Dots

Phenylalanine dehydrogenase (PheDH) which is categorized in oxidoreductase enzymescatalyzes the NAD+- dependent oxidative deamination of L-Phe to phenylpyruvate.This enzyme has widespread applications in industrial and medical fields such asdetermining the amount of phenylalanine for monitoring of phenylketonuria (PKU). Quantum dots (QDs) are known as semiconductors with many advantages including high photostability, unique optical characteristics, and symmetric emission spectrum.The protein-QD interactions have become an important interest due to its similarity with protein–ligand interactions. These interactions depend on many factors such as protein conformation and orientation and also can be lead to increase or decrease enzymatic activity due to NPs features.In this study, the interaction of B. badius Phenylalanine dehydrogenase (PheDH) and CdTe540 through examining of kinetic parameters of the enzyme for L-phenylalanine and L-tyrosine as substrateswereassessed to understand how this protein can interact with QD. After expression and purification of enzyme in prokaryotic E.coli BL21 host, kinetic parameters of the enzyme such as Km, Vmax, Kcat,Ki and Kcat/km values for L-Phenylalanine and L-tyrosine substrates in the presence and absence of CdTe540 were calculated. The results showed that CdTe could have an inhibitory effect on PheDH enzyme. Fluorescence spectroscopy demonstrated that the binding of QDs with enzyme induced conformational changes in the enzyme in the presence of CdTeQD. It was concluded that a comprehensive characterization of stability of enzyme bound QDs could be a necessary step in their potential use in biomedical fields.