SIMILARITIES IN THE INDUCTION OF SYNTHESIS OF A CELL‐SURFACE POLYPEPTIDE IN Arthrobacter sp. BY NEAR‐UV IRRADIATION and PHOTODYNAMIC CONDITIONS

Abstract

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.

“Light-derepressible” genes are regulated by metal-protein complexes: A hypothesis

“…Because the endogenous photoreceptor can be substituted in visible light by exogenous dyes, it probably functions as a sensitizer for a photodynamic reaction. Induction is blocked when the excited state of the photoreceptor is quenched by heroin and when the target of oxidation is protected by another, easily oxidized substance such as histidine (45). The characteristics of induction indicate that the process is initiated by a photooxidation reaction.…”

“…is induced when the Arthrobacter cells are exposed to near-UV light (45). When fully induced, this single polypeptide accounts for about 15% of total protein synthesis (20,43).…”

“…Among the most active dyes are methylene blue and its analogues (20,41). Methylene blue efficiently transfers energy in the excited state to molecular oxygen, but a number of experiments indicated that the highly reactive singlet oxygen generated by this reaction is not involved in induction of P21 synthesis (44,45). Addition of riboflavin, which readily undergoes one-electron, radical reactions, causes the cells to respond to blue light (41).…”

“…The characteristics of induction indicate that the process is initiated by a photooxidation reaction. Molecular oxygen and a photosensitizing pigment are required in addition to light (44,45). Visible light is ineffective in stimulating synthesis of P21 unless a dye is added to the cell suspension.…”

“…Another is synthesis of a single gene product, the subunit of pili, when cells of the prokaryote Arthrobacter sp. are exposed to light (20,41,44,45). Moreover, with the latter organism, transcription of this gene is induced in the dark when cells are treated with chelating agents or are exposed to a medium at pH 5 (43).…”