INTENSITY-DEPENDENT ENZYME PHOTOSENSITIZATION USING 532 NM NANOSECONDLASER-PULSES

The intensity dependence of the rose bengal (RB)-photosensitized inhib ition of red blood cell acetylcholinesterase has been studied experime ntally and the results compared to a quantitative excitation/deactivat ion model of RE photochemistry. Red blood cell membrane suspensions co ntaining 5 mu M RB were irradiated with 532 mm, 8 ns laser pulses with energies between 1 and 98.5 mJ. A constant dose (7 J) was delivered t o all samples by varying the total number of pulses. At incident energ ies greater than similar to 4.5 mJ/pulse, the efficiency for photosens itized enzyme inhibition decreased as the energy/pulse increased. The generation of RB triplet state was monitored as a function of laser en ergy and the triplet-triplet absorption coefficient was determined to be 1.9 x 10(4) M(-1) cm(-1) at 530 mn. The number of singlet oxygen mo lecules produced at each intensity was calculated from both the physic o-mathematical model and from laser flash photolysis results. The resu lts indicated that the photosensitized inhibition of acetylcholinester ase was exclusively mediated by singlet oxygen, even at the highest la ser intensities employed.