The quantum yields of photodynamic inactivation were determined for acetylated trypsin, carboxypeptidase, catalase, α-chymotrypsin, β-chymotrypsin, γ-chymotrypsin, δ-chymotrypsin, lysozyme, papain, peroxidase, ribonuclease, subtilisin, and trypsin by using methylene blue, eosin Y, and FMN as sensitizers. Reaction mixtures were buffered at pH 7.9 and maintained at 15°C while being illuminated with monochromatic light. With the exception of peroxidase, which was not inactivated at all under our experimental conditions, the quantum yields for the photodynamic inactivation of the different enzymes ranged from <tex-math>$1.0\times 10^{-7}$</tex-math> to <tex-math>$1.3\times 10^{-2}$</tex-math>. In general, the quantum yields for the inactivation of a given enzyme were largest with FMN, intermediate with eosin Y, and smallest with methylene blue. Within experimental error, the esterase and protease activities of the chymotrypsins and trypsins showed the same sensitivity to photodynamic treatment. Gamma-radiation inactivation yields for the above enzymes were also determined; yields with the different enzymes ranged from <tex-math>$1.7\times 10^{-5}$</tex-math> to <tex-math>$1.7\times 10^{-2}$</tex-math> molecule inactivated per electron volt of gamma radiation absorbed. The relative sensitivities to photodynamic treatment and to gamma radiation are roughly the same for most of the enzymes studied.

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