MECHANISM OF PHOTOSENSITIZATION BY PHEOPHORBIDE a STUDIED BY PHOTOHEMOLYSIS OF ERYTHROCYTES AND ELECTRON spIN RESONANCE SPECTROSCOPY

Abstract

Abstract Phcophorbide a (PPa), a causal substance of food intoxication, when excited by exposure to light wavelengths of over 600 nm, caused the photohemolysis of goat erythrocytes in proportion to the incubation time of the cells. The addition of N‐3, an effective scavenger of 1O2, to the medium markedly inhibited the hemolysis of erythrocytes in a concentration‐dependent manner, whereas the addition of superoxide dismutase (SOD) and catalase, inhibitors of O‐2 and H2O2 generation, respectively, to the medium had little effect on it.Methods for converting 1O2 to a nitroxide radical by 2,2,6,6‐tetramethyl‐4‐piperidone (TMPD) and for trapping O‐2 and OH by 5,5‐dimethyl‐l‐pyrroline‐A'‐oxide (DMPO) were employed to observe directly these activated oxygens by electron spin resonance (ESR). The methods provided evidence that only 1O2, was produced by PPa, which was excited by light wavelengths of over 600 nm. Both the addition of N3 to the solution and the removal of oxygen from the solution inhibited the generation of 1O2.These results led us to conclude that 1O2 was mainly responsible for the hemolysis of erythrocytes by photoexcited PPa.