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PHOTOCHEMICAL INACTIVATION OF TRYPSIN *
Author(s) -
Grossweiner L. I.
Publication year - 1974
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1974.tb06584.x
Subject(s) - chemistry , flash photolysis , photoionization , quantum yield , photochemistry , photodissociation , tryptophan , adduct , residue (chemistry) , reaction rate constant , fluorescence , ionization , kinetics , amino acid , organic chemistry , ion , biochemistry , physics , quantum mechanics
—The quantum yield for inactivation of aqueous trypsin fits the expression φ f =Σ r f r φ‘ r , where f r , is the fraction of incident light absorbed by residues of type r and the φ’ r are constants. The values φ‘ trp = 0.012, φ tyr = 0.005 and φ’ eys = 0.10, obtained at pH 3 in the wavelength range 240–290 nm, are attributed to independent events by comparing with quantum yields of the initial photochemical products and permanent residue destruction. The proposed inactivating processes are photoionization of one essential tryptophyl residue, photolysis of one essential cystyl residue, and splitting of an essential cystyl residue induced by light absorption in a nearby tyrosyl residue. The initial photochemical process from pH 3–7 identified by flash photolysis is the ejection of electrons from approximately two tryptophyl residues, leading to the formation of the disulfide bridge electron adduct and the hydrated electron. It is proposed that one photoionized tryptophyl residue is permanently disrupted and the other is restored through a back reaction that leads to a damaged, active enzyme form. An enhanced inactivation quantum yield at flash photolysis light intensities is attributed to a biphotonic process. A model based on one‐photon photoionization of tryptophan from a short‐lived precursor of the fluorescent state and the biphotonic photoionization of tryptophan via the triplet state is consistent with the experimental results.