Involvement of proteasomes (multicatalytic proteinase) in ATP-dependent proteolysis in rat reticulocyte extracts

The role of proteasomes, particles with latent multicatalytic proteinase, in ATP-dependent proteolysis in rat reticulocyte extracts was examined. Removal of proteasomes from the extracts by immunoprecipitation caused almost complete inhibition of ATP-dependent degradation of [3H]methylcasein, without affecting ATP-dependent proteolysis. Peptide fragments of [3H]casein, obtained by cyanogen bromide cleavage, were rapidly degraded in an ATP-independent fashion and this activity was not affected by removal of the proteasomes. These results suggest that proteasomes are involved in ATP-dependent proteolysis in the extracts and that they catalyze the initial cleavage of large proteins.