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Abstract
Information on the nature of alterations in the protein composition of the lens preceding the formation of nuclear cataracts in galactose-fed rats was sought in an investigation of a group of enzymatic proteins. Changes in the levels of five enzymes of carbohydrate metabolism were followed through the progressive phases of cataract development. A marked decrease in the activity (per lens) of aldolase occurs early in the first week of galactose feeding and appears to correlate with the vacuolization of the lens cortex. The other enzymes studied remain at control levels until a few days after the appearance of nuclear cataracts, at the end of the second week. They then decrease up to 50 per cent in activity when half of the total protein is lost from the lens. The sensitivity of an enzymatic protein to lens changes induced by galactose is probably influenced by its intrinsic metabolic stability, regional distribution, and subcellidar localization, but is not related to a sulfhydryl requirement for catalytic activity.