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.