Distribution of proteasomes and of the five proteolytic activities in rat tissues

Five peptidase activities (ChT-L, T-L, PGPH, BrAAP, and SNAAP) of the prote asome, and its caseinolytic activity, were measured in crude extracts of 10 rat tissues under experimental conditions simulating those found in vivo t hereby eliminating the alterations observed with the purified enzyme. The t otal and individual peptidase activities varied considerably from one tissu e to another, whereas the proteolytic activity measured with [C-14]methylca sein varied no more than twofold, The tissue-specific variations in individ ual peptidase activities may reflect tissue-specific differences in proteas ome subunit composition, or the presence of regulators. Immunological assay using an antibody directed against the iota (alpha 1) subunit showed that there was no correlation between protein abundance and peptidase activity. The results also show that the different peptidase activities are not repre sentative of proteasome distribution in the different tissues. (C) 2000 Aca demic Press.