Abstract
This paper considers the effect of aging on certain pathways of carbohydrate, protein, and nucleic acid metabolism in the normal lens. These alterations are related to experimental observations on the sugar cataracts and an attempt has been made to correlate the changes in metabolism occurring in the sugar cataracts with the altered activities of certain pathways associated with aging. The relationship between the age of the animal and the production of sugar cataracts may be due to the fact that the initial biochemical alterations involve pathways of glucose metabolism which are significantly affected by the aging process. Specific aspects of protein and nucleic acid metabolism in the normal lens also show a relationship to the aging process. These include changes in the relative concentrations of the soluble and insoluble (albuminoid) protein and RNA fractions and a progressive decrease in the amino acid-RNA and protein incorporating systems. Studies on the metabolism and chemistry of a cold precipitable protein (CPP) in the lens have shown that it consists of an aggregate of the three soluble lens proteins (alpha, beta, and gamma crystallins) in which there is a binding or coprecipitation of approximately 1 to 1.5 per cent RNA. Extensive metabolic and physicochemical studies suggest that this CPP may be an intermediate in the conversion of soluble to albuminoid lens protein.