PHOTOSENSITIZATION BY HYPERICIN - ELECTRON-SPIN-RESONANCE (ESR) EVIDENCE FOR THE FORMATION OF SINGLET OXYGEN AND SUPEROXIDE ANION-RADICALS IN AN IN-VITRO MODEL

The ability of hypericin (HYP) to photoreact by type I and type II mec hanisms was investigated in egg yolk lecithin (EYL) liposomes as a mod el membrane system. On visible irradiation in aerobic conditions at pH 7, the formation of singlet oxygen and superoxide anion radicals was demonstrated unequivocally using electron spin resonance (ESR) spectro metry with the spin traps 2,2,6,6-tetramethyl-4-piperidone (TEMP) and 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). We conclude from our results that HYP in EYL liposome membranes appears to act through both singlet oxygen and electron transfer mechanisms.