Abstract:

The interactions between bacitracin and lysozyme were studied by fluorescence spectroscopy. The results showed
that the intrinsic fluorescence of lysozyme could be quenched by bacitracin. The fluorescence quenching of lysozyme
was analyzed at different temperatures. The quenching mechanism was accomplished in a static manner by forming a
bacitracin-lysozyme complex. The binding parameters were determined according to Stern-Volmer equation, and the
thermodynamic parameters were calculated. The results showed that there was only one binding site between bacitracin and
lysozyme. The binding constants (KA) between bacitracin and lysozyme at different temperatures were 3.60 × 105 (298 K),
1.90 × 105 (308 K), and 4.51 × 104 L/mol (318 K), respectively. Thermodynamic analysis indicated that the interaction
process was spontaneous, and electrostatic force might be primarily responsible for the interaction. In addition, the effect
of bacitracin on the conformation of lysozyme was analyzed by three-dimensional fluorescence spectroscopy. The result
indicated that the polarity of the microenvironment around Trp residues decreased.

Key words: bacitracin, lysozyme, interaction, fluorescence spectroscopy