title: Probing the active site of trypsin with rose bengal: insights into the photodynamic inactivation of the enzyme.
abstract: In this work the active site of trypsin has been probed with the dye rose bengal. The dye binds competitively to the enzyme, and it can be used as a probe of the active site of the enzyme. On the basis of the emission wavelength, the binding site of trypsin is relatively polar and is similar to that of acetone in its polarity. The triplet state of rose bengal is quenched by trypsin. This quenching may be caused by the tryptophan and tyrosine residues that are in the near vicinity of the trypsin active site. This quenching can compete with the formation of singlet oxygen from the excited triplet state of rose bengal. We demonstrate that the singlet oxygen involved in the photoinactivation of trypsin is produced by the free rose bengal in solution and the bound dye is incapable of producing singlet oxygen. This explains the lack of correlation between photoinactivation efficiency and sensitizer binding capability previously reported by Wade and Spikes.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. mazdak@mail.med.upenn.edu
authors.forename: Mazdak
authors.initials: M
authors.lastname: Khajehpour
authors.forename: Thomas
authors.initials: T
authors.lastname: Troxler
authors.forename: Jane M
authors.initials: JM
authors.lastname: Vanderkooi
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D015394:Molecular Structure; D010777:Photochemistry; D012395:Rose Bengal / Q000737:chemistry* / Q000494:pharmacology*; D026082:Singlet Oxygen / Q000737:chemistry; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014357:Trypsin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D012997:Solvents; D026082:Singlet Oxygen; D012395:Rose Bengal; D014357:Trypsin