Regional and subcellular distribution of ascorbate free radical reductase activity in the human lens

This paper reports that the human lens is endowed with a characteristic regional and subcellular distribution of ascorbate free radical (AFR) reductase (EC 1.6.5.4) activity, and it is associated with the soluble fraction of the lens protein. AFR reductase activity in either immature senile cataractous or transparent lens was higher in the cortex, where the level of insoluble protein is lower, than in the nucleus. The high reductase activity and low insoluble protein content of the cortex were comparable between the assayed cataractous and transparent lenses. In the nucleus, in contrast, the reductase activity tended to decrease with an increase in the level of insoluble protein and with the development of nuclear coloration (sclerosis). As for the subcellular distribution of AFR reductase activity, 70-90% of the enzyme activity in the lens was located in the cytosol fraction. Based on the above results, it was proposed that cytosolic free radicals may be involved in oxidation, coloration and aggregation of lens protein in senile cataractogenesis and in lens aging.