Lysosome instability in aged rat brain.

The study of the age-dependent change in lysosomal enzyme activities of the cerebral tissue showed the significant increase of cathepsin D in the aged rat brain, while those of beta-glucuronidase and acid phosphatase remained unchanged. The subcellular distribution study of cathepsin D and beta-glucuronidase revealed the increased activity of these enzymes in the cytosolic fraction from the aged brain. In vitro incubation of the lysosome fraction from the aged rat brain resulted in more leakage of these two enzymes, indicating the instability of the lysosome in the aged brain, which resembled the effect of L-Leu-methyl ester to the lysosome.