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• W102417967 abstract "The kinetics of the dye-sensitized photoinactivation of trypsin were investigated. The time course of the trypsin inactivation as measured by the three assays could be fitted to first-order kinetics. The rates of trypsin inactivation were identical as measured by the casein and BAEE assays. A more rapid rate of inactivation was observed as measured by the Hb assay (containing 5M urea), using flavins as sensitizers, but not when methylene blue or eosin Y were used as sensitizers. These results were interprete by postulating the existence of a damaged'' class of molecules after irradiation which appears to be labile to 5M urea or to post-irradiation heating. A similar damaged class of molecules was observed during the inactivation of trypsin with gamma irradiation and self-digestion. The trypsin inactivation products were analyzed using the method of disc electrophoresis with columns of polyacrylamide gel, and by various other biochemical tests. A progressive loss of the trypsin bands was observed when the enzyme was inactivated by those procedures which produce a damaged class of molecules: flavin-sensitized photodynamic action, autolysis, ultraviolet irradiation, and gamma irradiation. No loss of the main trypsin more » band was observed when methylene blue and eosin Y were used as sensitizers. No changes were observed in the number of peptide bonds, free amino groups, or of chromogenic amino acid sequence after the photoinactivation of trypsin as sensitized by flavins and methylene blue. Some photobleaching was observed with the three dyes during the photodynamic reaction; in spite of this, the time course of the inactivation of trypsin remained first-order within experimental error. Deviations from first-order kinetics were observed for the flavin- sensitized photoinactivation of ribonuclease when the irradiation period was extended. It was found that trypsin had a protective'' effect on the amount of photobleaching of flavins in air and in a nitrogen atmosphere. Methylene blue showed this effect in a nitrogen atmosphere only. The time course of the photodynamic reaction was also followed by measuring the amount of oxygen consumed. The results obtained indicated that the assumption of a stoichiometric relation between the oxygen consumed and the amount of enzyme activity lost may not be valid. However, the present results were far from satisfactory. A possible way of obtaining significant data and a method of analysis of the data were indicated so that a comparison could be made with trypsin photoinactivation kinetics. In a few preliminary experiments along these lines it was found that the ratio of the initial rate of oxygen consumption to the initial rate of trypsin inactivation on the illumination varies greatly with the dye used. The ratio is 59 with methylene blue and 393 with riboflavin. These data lend strong support to the conclusion that the mechanisms of these two photodynamic reactions are different. On the basis of a comparative study of the dye concentration, enzyme concentration, pH-dependence, and oxygen consumption studies of the photoinactivation of trypsin as sensitized by flavins, eosin Y, and methylene blue, it was concluded that the mechanism of the photodynamic reaction was different for each of the three sensitizers. In addition, the kinetics of the flavinsensitized photoinactivation of trypsin were found to be markedly different at pH 5 and 8, thus suggesting that the mechanism of this reaction may depend on pH. The kinetics of the dye-sensitized photoinactivation of trypsin experi- mentally obtained were compared with four main types of mechanisms which have been proposed to explain photodynamic action. The present results do not conform to any one of the mechanisms proposed. It is therefore concluded that photodynamic action is probably a class of reactions, the mechanism depending on the reaction conditions and on the sensitizer dye used. (auth) « less" @default.
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• W102417967 date "1963-09-01" @default.
• W102417967 modified "2023-09-27" @default.
• W102417967 title "PHOTOINACTIVATION OF TRYPSIN AS SENSITIZED BY FLAVINS, METHYLENE BLUE AND EOSIN Y" @default.
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