Interaction mechanism between berberine and the enzyme lysozyme

In the present paper, the interaction between model protein lysozyme (Lys) and antitumorigenic berberine (BBR) was investigated by spectroscopic methods, for finding an efficient and safe photosensitizer with highly active transient products using in photodynamic therapy study. The fluorescence data shows that the binding of BBR could change the environment of the tryptophan (Trp) residues of Lys, and form a new complex. Static quenching is the main fluorescence quenching mechanism between Lys and BBR, and there is one binding site in Lys for BBR and the type of binding force between them was determined to be hydrophobic interaction. Furthermore, the possible interaction mechanism between BBR and Lys under the photoexcitation was studied by laser flash photolysis method, the results demonstrated that BBR neutral radicals (BBR(-H)center dot) react with Trp (K = 3.4 x 10(9) M-1 s(-1)) via electron transfer to give the radical cation (Trp/NH center dot+) and neutral radical of Trp (TrpN center dot). Additionally BBR selectively oxidize the Trp residues of Lys was also observed by comparing the transient absorption spectra of their reaction products. Through thermodynamic calculation, the reaction mechanisms between (BBR)-B-3* and Trp or Lys were determined to be electron transfer process. (c) 2012 Elsevier B.V. All rights reserved.