Comparison study on the interaction mechanisms of B. amyloliquefaciens amylase with PEG-400 and TEPA and the properties of enzyme

• PEG-400 showed a stronger promoting effect on the operation of BAA than TEPA.
• Intrinsic fluorescence of BAA was quenched or enhanced by TEPA or PEG-400.
• PEG-400 reduced the polarity in surrounding of Tyr residues.
• TEPA enhanced the polarity in the regions around Trp residues.
• PEG-400-BAA interaction was due to hydrophobic interaction and hydrogen bonding.
• TEPA-BAA interaction was due to van der waals force and electrostatic interaction.

The activity of BAA can be maximally increased about 1.68 times and 1.23 times in the presence of 3.6% (w/v) PEG-400 and 0.2% (w/v) TEPA, respectively. Compared to TEPA, PEG-400 addition can improve the activity of BAA at higher temperature. The addition of PEG can result in enhanced fluorescence of BAA but showed no influence on the UV spectra. Whereas, the presence of TEPA can not only reduce the fluorescence of BAA through dynamic quenching mechanism but also enhance the UV adsorption of BAA at 220 nm and shifted absorption peak from 265 nm to 290 nm. Synchronous fluorescence studies found PEG-400 can reduce the polarity in the environment around the Tyr residues, while TEPA addition can enhance the polarity in the microenvironment around the Trp residues. The hydrophobic interaction and hydrogen binding existed in the interaction between BAA and PEG-400 rendered the enzyme more stable. The ionic interaction and van der waals force between TEPA and BAA can maintain the optimum enzyme activity in a wider pH range. The addition of PEG-400 demonstrated a larger promoting effect on the activity of BAA compared to that of TEPA addition.

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