The interaction between hypocrellin A and tryptophan was studied by electron absorption and fluorescence spectroscopies and by flash photolysis. The mechanism of hypocrellin A-sensitized photooxidn. of tryptophan was investigated by a quenching test, deuterium substitution, and solvent effect. The reaction proceeds via competition between electron transfer and singlet O, the latter being the major process. The influence of the circumstances on the reaction was also investigated. There are 4 factors i.e. the concentration of substrate, the concentration of dissolved O, the nature of solvent and pH value of solution, which exhibit strong effects on the reaction.

Key words: FLUORIMETRIC ANALYSIS, INDOLE P, TRYPTOPHAN, ABSORPTION SPECTROMETRY, DERMATOSIS, SOLVENT EFFECT, PHOTOSENSITIZATION OXIDATION, HYPOCRELLIN A