Methionine adenosyltransferase and S-adenosylmethionine in the developing rat lens

Methionine adenosyltransferase (MAT) activity, and the concentration of its reaction product, S-adenosylmethionine (AdoMet), were measured in the lenses of rats of different ages; ranging from 1 day of age to over 1 yr. The highest specific activity of MAT was found in the lenses of the one day old rats (sp. ac. 0.327 units/mg-1 protein). After 1 week the specific activity had dropped to 0.067, and by 6 weeks had declined to adult levels (0.02 units/mg-1 protein). AdoMet concentrations were measured by HPLC in perchloric acid extracts. The highest concentration of AdoMet was found in the lenses of day-old rats (48.2 microM), and gradually declined with increasing age, reaching 5.5 microM in the oldest rats. In addition, the specific activity of MAT was found to be higher in the lens epithelium than in the cortex plus nucleus. The specific activity of MAT is almost an order of magnitude higher in the lens epithelial fraction (0.099 units mg-1 protein) than in the combined cortex plus nucleus fraction (0.011 units mg-1 protein).