EFFECTS OF QUENCHING AGENTS ON THE PHOTODYNAMICALLY‐INDUCED CHEMOTACTIC RESPONSE OF THE COLORLESS FLAGELLATE Polytomella magna

Publisher Website
Google Scholar
Abstract
In the presence of the photosensitizer riboflavin at high fluence rates a photoproduct, most probably H2O2, is formed which causes negative phototaxis in the colorless flagellate Polytomella magna. The aim of this study was to find out whether H2O2 is produced in a type I or II reaction. As has been shown, 1O2 quenchers either do not influence the photodynamic action of riboflavin (furfuryl ethanol, DPBF, l‐histidine, crocetin) or show slight quenching effects only at very high concentrations ≧ 10−2M (DABCO, DMF, imidazole). D2O is toxic to P. magna even in 1:1 and 1:2 mixtures with H2O. On the other hand, the quenching effect of 1,4‐benzoquinone, highly indicative for the type I pathway, is more than two orders of magnitude stronger than the one of the above mentioned 1O2 quenchers. The results suggest that H2O2 is produced in a type I reaction. Superoxide does not seem to be involved since superoxide dismutase does not diminish the photodynamic effect of riboflavin.