Worm Breeder's Gazette 9(3): 120
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
The accumulation of altered or damaged enzymes in aging organisms, first observed in Turbatrix aceti by Gershon & Gershon, has also been found to occur in mammals. It has been suggested that this accumulation may result from an age-dependent decline in the ability of cells to degrade these abnormal proteins. Sharma et al. [1979] and Prasanna & Lane [1979] reported an age-dependent decline in turnover rates in T. aceti, both for specific enzymes and for global protein. The measurement of protein turnover is fraught with technical difficulties and we know very little about the enzymatic mechanisms involved. One simple hypothesis to explain declining rates of turnover in older animals is that the amount of cellular protease activity also declines with age, leading to a decreased capacity for intracellular proteolysis. We have found that the activities of several lysosomal proteases decline markedly in aging C. vity of the major aspartyl protease cathepsin D declines about 10-fold from its peak at 4 days of age (growth at 25 C; mean lifespan about 12 days) to a minimum at about 10-11 days. Both the total activity per animal and the specific activity (per unit protein) decline. Immunoblot analysis using anti-cathepsin D antibody shows that this activity loss is accompanied by a parallel loss of cathepsin D measured as antigen. Using enzymatic assays after isoelectric focusing of crude extracts, we have also measured the age-dependence of the thiol cathepsins Ce1 and Ce2 (see Sarkis et al ., this issue) which hydrolyze Z-phe-arg- aminomethylcoumarin. From day 3 to day 11, the specific activity of cathepsin Ce2 declines about 8-fold, whereas that of cathepsin Ce1 declines about 2.5-fold. These experiments also revealed a previously undetected enzyme which hydrolyzes the same substrate, but has a different isoelectric point from those of Ce1 and Ce2. On the basis of IEF analysis of purified lysosomes, this new enzyme is nonlysosomal. Its specific activity is essentially independent of the age of the animals. The age-dependent decrease in lysosomal protease activities is quite different from the strong (as much as 100-fold) increase in lysosomal glycosidase and phosphatase activities (Bolanowski et al., 1983). We think it possible that the decrease in protease levels is causally related to the increase in other lysosomal enzyme levels, since the cad-l mutant which is deficient in cathepsin D has abnormally elevated levels of -hexosaminidase and -glucosidase at all ages. It would not be surprising if lysosomal glycosidases were at risk for proteolysis while cohabiting with proteases. The age- dependent declines in lysosomal protease activities are at least consistent with the possibility that there is a simple enzymatic basis for decreasing protein turnover capacity in aging animals. We emphasize, however, that there is still no direct evidence that these Iysosomal enzymes are principally responsible for intracellular protein turnover.