Age changes in bovine lens endopeptidase activity

Lens endopeptidase activity and thermal stability have been determined as a function of cell development, cell age, and animal age. Lenses from animals aged 3 months to 15 years (lens weights 1.15-2.80 g) were divided into epithelial (outermost), cortical (peripheral), and nuclear (central) regions. Changes accompanying cell development were determined by measuring specific activity in epithelial (undifferentiated), outer cortical (differentiating), inner cortical (mature) and nuclear (aged) regions of individual lenses. Thermal stability of the enzyme activity obtained from the outer cortical and nuclear regions of the same lenses was also determined. Specific activity and thermal stability were found to decrease as a function of lens cell development. Changes with cell development represent the effects of both differentiation and increasing cell age. To determine the effects of cell age alone, activity was determined in the same population of aged, fully differentiated cells in lenses of different ages. Specific activity decreased as a function of cell age alone. Changes with animal age were determined by comparing cells of the same developmental stage from animals of different ages (e.g., differentiating cells of the cortex in animals 3 months to 15 years old). Specific activity for the cortical region increased with animal age while specific activity in the nuclear region appeared to remain constant or decrease slightly with increasing animal age. Thermal stability of the enzyme activity from the cortex was different in young and adult lenses. The change in stability occurred early in the lifespan and was therefore more closely related to animal development than to aging.