Glycation and insolubility of human lens protein.

To learn whether glycation plays a role in insolubilization or in senile cataractogenesis, the reactivity of lens protein from normal and senile cataractous lenses and individual crystallin prepared from human lens with various sugars glucose, glucose-1-phosphate (G-1-P), glucose-6-phosphate (G-6-P) and fructose], and the insolubility of those proteins were determined. The reactivity of human lens protein to glucose was increased in a dose-dependent manner, and it was demonstrated that 17.9, 18.5 and 24 kDa proteins were susceptible to glycation with sugars. The study also showed that alpha-, beta-crystallins and high molecular weight (HMW) aggregate obtained from cataractous lens have some weak reactivity against sugars. It was demonstrated that the proteins obtained from normal lens of older age and from cataractous lenses have higher insolubilities to glucose than do normal younger ones. Measurement of glycosylated protein by affinity column chromatography revealed that cataractous lenses contained a larger amount of glycosylated protein than normal ones. These results suggest that there is an age-related increase of glycation in normal human lens protein, and that such glycation increases the amount of insolubilized protein with the effect of aging. The author also speculates that an abnormal acceleration of glycation in the human lens may induce senile cataract formation.