ALTERATION OF RAT-LIVER 20S PROTEASOME ACTIVITIES BY AGE AND FOOD RESTRICTION

The effects of age and food restriction on proteasome function in rat liver supernatant (100,000 x g) were investigated. The cellular level of the proteasome has been quantitated by using Western blot analysis. The level of the proteasome was not affected by either age or food re striction. The three best-characterized proteasomal peptidase activiti es, chymotrypsin-like (ChT-L), trypsin-like (T-L), and peptidylglutamy l peptide hydrolying (PGPH) activities, were measured in the presence and absence of the proteasomal activator, sodium dodecyl sulfate (SDS) . Basal ChT-L, T-L, and PGPH activities were not markedly affected by either age or food restriction. SDS-stimulated ChT-L and T-L. activiti es increased approximate to 15% and approximate to 30%, respectively, between 7 and 26 months of age, and the increase of befit activities w as prevented by food restriction. In marked contrast, the SDS-stimulat ed PGPH activity decreased approximate to 40% with age. Food restricti on, while not preventing the age-related decline, maintained higher le vels of SDS-stimulated PGPH activity at all ages. The proteolytic acti vity of the proteasome toward casein was not altered by either age or food restriction. In conclusion, the cellular level of the proteasome as sell as the caseinolytic activity of the proteasome appear to be un affected by either age or food restriction. It appears unlikely that t he proteasome activity changes are related to the reported age-associa ted decline of protein degradation. Simultaneously, proteasomal peptid ase activities appear to be differentially regulated by both age and f ood restriction. It suggests more subtle age-related changes in protea some function, which could include an effect on proteasomal subunit co mposition.