Accumulation of inactive cathepsin D in old rats

From the 2nd to the 29th month of life seven different rat organs (liver, heart, kidney, lung, spleen, skeletal muscle, intestinal mucosa) show a continuous increase in the concentration of protein reacting with rabbit antiserum against rat liver cathepsin D. However, the activity of aspartate proteinases, probably mainly cathepsin D, does not show the same increase. This result is interpreted as accumulation of enzymatically inactive but immunologically reactive cathepsin D. This phenomenon, which is well known for some cytosolic enzymes in senescent animals, is first reported to occur for a lysosomal proteinase as well.