Physiological and genetic implications of selective mutation by light at 320-400 nm

Flavone photoreactivity. UV-induced reactions in organic solvents and micellar systems

Flavonoid photochemistry is a subject of interest in studies dealing with the role of phenolic compounds as screening pigments in plants. In order to contribute to the understanding of the processes involved in the interaction between flavonoids and UV radiation, we have studied UV-induced flavone photodegradation in both organic solvents and micellar systems. The results obtained show that flavone photosensitivity depends on the characteristics of the reaction environment and is influenced by the medium polarity and the charges on the micellar surface. Qualitative and quantitative differences in the photodegradation products were demonstrated by high performance liquid chromatography (HPLC) analysis.

Effect of near-ultraviolet and visible light on mammalian cells in culture II. Formation of toxic photoproducts in tissue culture medium by blacklight

Near-ultraviolet radiation was found to be lethal for mammalian cells in Dulbecco's modified Eagle's medium without serum or phenol red. Irradiation of the cells with near-ultraviolet light while the cells were in phosphate-buffered-saline abolished the lethal effect. When only the medium was irradiated followed by the addition of unirradiated cells and serum, the cells were still killed. The photoactive components of the medium for this effect were riboflavin, tryptophan, and tyrosine. When riboflavin was deleted from the medium being irradiated and added later, almost no killing was detected. Irradiation of salt solution of riboflavin and tryptophan or riboflavin and tyrosine, resulted in cell killing. Little or no killing resulted when riboflavin, tryptophan, or tyrosine was irradiated singly. The formation of photoproducts toxic for mammalian cells appears to involve photodynamic action. Experiments utilizing Dulbecco's or similar media without proper controls may produce anomalous results from light illuminating the laboratory.

Lethal and mutagenic action of black light (325 to 400 nm) on Haemophilus influenzae in the presence of air

Near-ultraviolet (UV) light (325 to 400 nm), in the presence of air and the absence of exogenous photosensitizing compounds, is lethal and mutagenic for Haemophilus influenzae. The lethal effect is the same for both wild type and streptomycin-resistant mutants, indicating that the mutants are not selected by the irradiation. The inactivation and mutagenicity show a large shoulder, suggesting the existence of repair systems. Filters were used to eliminate the possibility of short-UV irradiation. The effective radiation is between 325 to 400 nm. The lethal and mutagenic effects are higher during mid and late log phase than during early log or stationary phase.