Abstract
Various dyes were tested in order to compare photosensitizing ability based on relative quantum yield for photosensitized oxidation of histidine. Each dye belongs to such u class as thiazine, xanthene, acridine, thiazole, phenylmethane, monoazo, azine, oxazine, porphylline and flavin. The heterocyclic structure was essential to the development of photosensitizing ability, but this ability was remarkably influenced by introduction of substituents on aromatic rings. Fluorescence was not always accompanied with photosensi-tization.
Except for fluoresceine, each dye had a common feature as to pH dependence of photosensitized oxidation of histidine, and this reaction was dependent on electrical charge of imidazole group of histidine. Each dye also showed a common behaviour on Line-weaver-Burk's plots. Using various dyes, the photosensitized oxidation of histidine was compared with that of tryptophan, and it was found that the ratio of raction rates of both amino acids was varied with the kinds of dye. For example, the reaction rate of tryptophan was only one forth of that of histidine in the case of thionine, while in eosine no difference was shown between the reaction rate of both amino acids.
