Assessment of polystyrene nano plastics effect on human salivary α-amylase structural alteration: Insights from an in vitro and in silico study

The study found that the enzyme activity of human salivary α-amylase (α-AHS) was competitively inhibited by nanoplastic polystyrene (PS-NPs), with a half-inhibitory concentration (IC50) of 92 μg/mL, while the maximum reaction rate (Vmax) remained unchanged at 909 μg/mL•min. An increase in the concentration of PS-NPs led to a quenching of α-AHS fluorescence with a slight red shift, indicating a static mechanism. The binding constant (Ka) and quenching constant (Kq) were calculated to be 2.92 × 1011 M−1 and 1.078 × 1019 M−1• S−1 respectively, with a hill coefficient (n) close to one and an apparent binding equilibrium constant (KA) of 1.54 × 1011 M−1. Molecular docking results suggested that the interaction between α-AHS and PS-NPs involved π-anion interactions between the active site Asp197, Asp300 residues, and van der Waals force interactions affecting the Tyr, Trp, and other residues. Fourier transform infrared (FT-IR) and circular dichroism (CD) analyses revealed conformational changes in α-AHS, including a loss of secondary structure α-helix and β-sheet. The study concludes that the interaction between α-AHS and PS-NPs leads to structural and functional changes in α-AHS, potentially impacting human health. This research provides a foundation for further toxicological analysis of MPs/NPs in the human digestive system. [Display omitted] •Assessment of PS-NPs effects on α-AHS was investigated in the microenvironment system.•The PS-NPs against α-AHS inhibition activity and enzyme kinetics were performed.•The inhibition efficiency of IC50 was used to determine the competitive inhibition type.•A static quenching mechanism and affected amino acid residues were shown by fluorescence spectroscopy.•An in silico Molecular Docking study was determined to affect aromatic residues and confirmational structural alteration.