Intensity‐Dependent Enzyme Photosensitization Using 532 nm Nanosecond Laser Pulses

Abstract— The intensity dependence of the rose bengal (RB)‐photosensitized inhibition of red blood cell acetylcholinesterase has been studied experimentally and the results compared to a quantitative excitation/deactivation model of RB photochemistry. Red blood cell membrane suspensions containing 5 μM RB were irradiated with 532 nm, 8 ns laser pulses with energies between 1 and 98.5 mJ. A constant dose (7 J) was delivered to all samples by varying the total number of pulses. At incident energies greater than ∼ 4.5 mJ/pulse, the efficiency for photosensitized enzyme inhibition decreased as the energy/pulse increased. The generation of RB triplet state was monitored as a function of laser energy and the triplet‐triplet absorption coefficient was determined to be 1.9 × 104M−1 cm−1 at 530 nm. The number of singlet oxygen molecules produced at each intensity was calculated from both the physico‐mathematical model and from laser flash photolysis results. The results indicated that the photosensitized inhibition of acetylcholinesterase was exclusively mediated by singlet oxygen, even at the highest laser intensities employed.

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