Aspartic acid racemisation in the human lens during ageing and in cataract formation

Abstract

D-ASPARTIC acid has been shown to accumulate with age in human tooth enamel¹ and dentine² at a rate of about 0.1% yr⁻¹. We have predicted that racemisation should take place in any metabolically stable protein in long-lived mammals and that, as a consequence of racemisation, these proteins will have altered conformations which would probably produce changes in their biological activities or chemical properties³. We have extended these studies to soft tissue proteins, in particular those in the human lens. The proteins in the central portion of the lens are among the most stable in the human body⁴. Numerous changes in the properties of the lens proteins occur with age and cataract formation—denaturation⁵, increasing pigmentation⁶, cross linking^5,6 insolubility^6–9, and fluorescence¹⁰. Pirie¹¹ has suggested that physicochemical processes may be responsible for these changes. We report here the results of D/L enantiomeric analyses of normal human lenses and cataracts: aspartic acid racemisation was seen during ageing and cataract formation.