The efficiency of photodynamic treatment with thiopyronine (TP) on the respiration and fermentation of yeast cells, on the metabolic oxygen uptake of isolated mitochondrial preparations from yeast, and on the enzyme activity of alcohol dehydrogenase (ADH) in vivo and in vitro were studied. Respiration was inactivated by treatment with TP and visible light more at the initial stage than was the fermentation. Isolated mitochondria and ADH in vitro were not as sensitive to treatment as were respiration and fermentation in vivo. Inactivation patterns of respiration and fermentation in vivo showed that the inactivation was not due to damage to the DNA. The hindrance of respiration and fermentation might be one of main causes of cell-death resulting from photodynamic treatment.

The treatment of yeast with thiopyronine (TP) caused a degradation of polyribosomes, even if the cells were not illuminated. In contrast, no differences in the polyribosome profiles of illuminated and unilluminated cells could be seen. Likewise, in in vitro experiments, there was no degradation of polyribosomes caused by dark effect or photodynamic action. Cell-free protein synthesis was inhibited up to 75 per cent by the photodynamic effect when the complete system was treated, but only up to 40 per cent when the polyribosomes or enzyme fraction were treated. Since the enzyme fraction contained aminoacyltRNA-synthetases and tRNA, it was necessary to investigate separately the effect of TP on the enzyme and the tTNA. It was shown that the aminoacyl-tRNA-synthetase and not tRNA was effected by the photodynamic action in its biological activity.

The photodynamic inactivation of a cell-free transcriptional system with yeast components was investigated in vitro. The photodynamic inhibition of the overall synthesis is dependent on the irradiation time and is due to the photo-oxidation of the DNA as well as of the RNA polymerase. Photodynamic treatment of the polymerase and DNA together leads to a stronger inactivation of their biological activity than photodynamic treatment of both components separately. Also the rate of RNA synthesis is more affected when the complete system is photodynamically treated shortly after beginning than before beginning of RNA synthesis. It is concluded that the polymerase-DNA complex is more sensitive to photo-oxidation than the individual components. Because the steps binding and initiation do not seem very affected photodynamically it is suggested that the Thiopyronine-sensitized inhibition of RNA synthesis is mainly due to an inhibition of elongation.