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Mechanism of Photoinduced Carotenoid Synthesis

INDUCTION OF CAROTENOID SYNTHESIS BY ANTIMYCIN A IN THE ABSENCE OF LIGHT IN MYCOBACTERIUM MARINUM

From the ¹ From the Department of Biology, Wright State University, Dayton, Ohio 45431

Mycobacterium marinum, like a number of nonphotosynthetic microorganisms, produces only traces of carotenoids when grown in the dark. On illumination, the dark grown bacteria synthesize substantial amounts of carotenoids de novo. This study shows that antimycin A can also induce the synthesis of carotenoids in M. marinum in the absence of light. The amounts of carotenoids synthesized are proportional to the amount of antimycin A added; for maximal carotenogenesis, a concentration of 37.5 µm is required.

Antimycin A is 300 to 400% more effective than saturating amounts of light in the induction of carotenoid synthesis. The effects of light and antimycin A are additive. Chromatography of the carotenoid pigments reveals that the same polyenes are synthesized regardless of the means of induction—light alone, antimycin A in the dark, or antimycin A plus light.

Evidence is presented that both light and antimycin A act by inducing protein synthesis (carotenogenic enzymes). In the antimycin A-induced system protein synthesis continues for more than 20 hours. In the light-induced system, on the other hand, protein synthesis continues for 4 hours and then stops. However, a second illumination at this time can lead to a resumption of protein synthesis.

Inasmuch as the inductive effects of light and antimycin A are additive, it is concluded that the sites of action of light and antimycin A are different. Antimycin A may act either as an inducer for the synthesis of carotenogenic enzymes or by inactivating a repressor. Light may have an analogous role but at a different site; it may act either by photo-oxidizing a repressor or by producing a photo-oxidized metabolite which can act as an inducer for the synthesis of carotenogenic enzymes.

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