Paramagnetic Species in Cataractous Human Lenses.

摘要

Current theories implicate near ultraviolet (UV) light in the cataractous process. The present study was undertaken to identify the phosphorescent species in the human lens after UV radiation. Cataractous lenses were obtained at surgery and noncataractous lenses were obtained at autopsy. Using electron spin resonance spectroscopy, the writers characterized the UV light-induced paramagnetic triplet state of normal and cataractous lenses, and offer unequivocal proof that it stems from the tryptophan moiety. At 133 K, the phosphorescence in both normal and cataractous lenses was found to have a lifetime of 4.0 + or - 0.1 sec. This was interpreted to reflect a similar microenvironment for the tryptophan residue in both normal and cataractous lenses. Finally it was discovered that the lens excited triplet (phosphorescent) tryptophan is apparently a precursor to a free radical; this free radical may be the missing link between ultraviolet (UV) irradiation and lens photodamage leading to cataract formation.