Replacement of riboflavin by an analogue in the blue-light photoreceptor of Phycomyces.

Under suitable conditions, roseoflavin [7-methyl-8-dimethylamino-10-(1'-D-ribityl)isoalloxazine] replaces riboflavin to about 80% in the photoreceptor of Phycomyces. The substitute-bearing photoreceptor functions with an efficiency of about 0.1% of that of the normal receptor. The substitution is proven by (i) a decrease of the effective light flux by a factor of 4.7, expressed as a corresponding increase in threshold, and (ii) an increase of the effectiveness of 529-nm light relative to 380-nm light. It has also been shown that roseoflavin is taken up by the mycelium, translocated to the sporangiophore, and effectively phosphorylated by the riboflavin kinase of Phycomyces.