Properties of 26S proteasome purified from rat skeletal muscles: comparison with those of 26S proteasome from the rat brain.

A ubiquitin/ATP-dependent proteolytic complex (26S proteasome) was highly purified from rat skeletal muscles and its enzymatic properties were compared with those of the brain 26S proteasome. The purified 26S proteasome comprises 22-110 kDa subunits characteristic of the typical 26S proteasome on the basis of SDS-PAGE. The two-dimensional PAGE (NEPHGE and SDS-PAGE) pattern revealed that the pI values and molecular masses of the muscle 26S proteasome subunits were similar but not identical to those of the subunits of 26S proteasome purified from the rat brain. The enzymatic properties of the muscle 26S proteasome were very similar to those of the brain enzyme in substrate specificity and inhibitor susceptibility. The specific activities of the muscle 26S proteasome toward three fluorogenic peptide substrates were indistinguishable from those of the brain enzyme.