Abstract—
Synthesis of a 21000‐dalton polypeptide is greatly stimulated in a species of Arthrobacter by the combined influence of light, oxygen and a sensitizing dye. The dye must enter the cells for the effect to occur. The extent of photoinduction was not enhanced in the presence of D2O nor was it significantly inhibited by 10–20 mM azide or 1,4‐diazabicyclo [2.2.2]octane. The phenazine dye neutral red was nearly as effective as methylene blue and rose bengal in sensitizing photoinduction, although neutral red was inactive as a sensitizer of the photooxidation of histidine or methionine, singlet oxygen‐mediated reactions. Thus, generation of singlet oxygen does not seem to be a necessary step in the mechanism of induction. Neutral red had low activity as a sensitizer of the oxidation of sulfite, which proceeds by a radical mechanism. Considering also the known properties of phenazine compounds, the evidence supports the involvement of radical intermediates in the mechanism of photoinduction. Furthermore, the results suggest that the dyes must interact directly with an intracellular component, possibly DNA, for induction to occur.
Irradiation of aerobic suspensions of Arthrobacter sp. with near‐UV light (310‐400 nm) induced synthesis of a 21 000 dalton, cell‐surface polypeptide. Synthesis of this polypeptide also was induced by visible light in the presence of photodynamic dyes, as shown previously (Hoober, 1978). Induction of the polypeptide in near‐UV light and with visible light plus dyes was inhibited by histidine. Hemin inhibited induction in near‐UV light and in visible light with methylene blue, neutral red and acrifiavin, which are cationic dyes, but failed to inhibit induction in visible light with rose bengal, an anionic dye. These results suggested that inhibition by hemin required electrostatically favored interaction between the anionic porphyrin and the sensitizer, and that the near‐UV light effect was mediated by a cationic or neutral endogenous sensitizer. The similarities in the responses of the cells to near‐UV irradiation and visible light plus dyes suggested that the mechanism of induction under the two conditions was the same.
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