RED LIGHT-INDUCED ACCUMULATION OF EUGLENA GRACILIS

Abstract— It has been shown that green cells of Euglena gracilis accumulate under red light. The action spectrum of this response has been determined. Its shape and the results of regreening experiments clearly indicate a role of chlorophyll. The quenching effect of chlorophenyl–dimethylurea and NH₂OH demonstrate that this cell accumulation is not directly light-induced, as in the case of phototaxis, but is due to an effect of oxygen, the evolution of which is stimulated by light.     

METABOLISM OF 5-METHOXYPSORALEN BY Saccharomyces cerevisiae

Incubation of methoxypsoralen (5-MOP) in the presence of diploid yeast cells (Saccharomyces cerevisiae) before UV-A exposure leads to an incubation-time dependent decrease of photoinduced genotoxic effects. The reduction in photoinduced genotoxicity is stronger in cells grown in the presence of 20% glucose and containing high levels of cytochrome P-450 than in cells grown in the presence of 0.5% glucose and containing undetectable levels of cytochrome P-450. Inhibition of P-450 activity by specific inhibitors, such as tetrahydrofuran and metyrapone, strongly affects the observed decrease in 5-MOP genotoxicity, indicating the involvement of P-450 in 5-MOP metabolism. As demonstrated by spectrophotometric and chromatographic (HPLC) analysis during incubation of 5-MOP with P-450 containing yeast cells, 5-MOP gradually disappears from the cell supernatant of the incubation mixture. The reduction in the chromatographic peak corresponding to 5-MOP is accompanied by the appearance of a new peak that probably corresponds to a metabolite. As shown by the use of P-450 specific inhibitors, the metabolite appears to be due to P-450 mediated 5-MOP metabolisation. Its UV absorption spectrum suggests an alteration of the pyrone moiety of the 5-MOP molecule.