Interaction mechanism between berberine and the enzyme lysozyme

► Static quenching is the main fluorescence quenching mechanism between Lys and BBR, and there is one binding site in Lys for BBR. ► BBR neutral radical react with Trp (K = 3.4 × 109 M−1 s−1) via electron transfer to give the radical cation (Trp/NH
- +) and neutral radical (TrpN
- ) of Trp. ► BBR can selectively oxidize the Trp residues of Lys with the rate constant 4.2 × 108 M−1 s−1. ► Through thermodynamic calculation, the reaction mechanisms between 3BBR∗ and Trp or Lys were determined to be electron transfer process.