LAUSR

Abstract In this investigation, the structure and stability of acid phosphatase against TiO2 nanoparticles were investigated via enzyme activity assay, fluorescence spectroscopy, thermal stability, and circular dichroism spectroscopy techniques. The acid phosphatase activity showed that the TiO2 nanoparticles combination inhibited the enzyme activity in the form of a non-competitive inhibition. The value of dissociation constant ( K i ) was computed to be 0.258 at 310 K . By raising the nanoparticles concentration, the thermal stability was reduced from 342 to 338 K. Far-UV circular dichroism studies also illustrated that TiO2 nanoparticles could alter the secondary structure of acid phosphatase through an increase in the content of the α -helix structure (from 10.8 % to 14.9 % ) and a decrease in the β -sheet (from 30.2 % to 27.4 % ). The Stern-Volmer constant was declined from 6.4 × 10 4 to 5.5 × 10 4 M−1 with raising the temperature. It was also revealed that TiO2 nanoparticles decreased the intrinsic fluorescence of acid phosphatase via the static quenching mechanism. The binding process was spontaneous, and the thermodynamic parameters also demonstrated the van der Waals and hydrogen bond interactions between TiO2 nanoparticles and acid phosphatase. Therefore, TiO2 nanoparticles could influence acid phosphatase stability and activity.