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Abstract
The incorporation of U-14C glutamic acid into soluble bovine and human lens protein fractions has been studied as a function of age. Culture technique and DEAE cellulose fractionation has been used. In bovine lenses the incorporation of glutamic acid into alpha and gamma crystallins decreased with age whereas in the beta crystallin group the specific activities remained constant. All protein fractions of the human lenses showed a gradual reduction of the incorporation of the radioactive amino acid between 40 and 74 years of age. The highest specific activity was found to correspond to Spector's HL protein and its existence is confirmed throughout the whole human life-span.