Purification and characterization of 20 S proteasome from wheat leaves

The 20 S proteasome (multicatalytic proteinase) from wheat leaves was purified to apparent homogeneity by successive chromatographies steps. The molecular mass of the purified proteasome complex was estimated to be 580 kDa by gel filtration. Polyacrylamide gel electrophoresis of the proteasome gave a single protein band under non-denaturing conditions and at least ten bands in the range 20-32 kDa in the presence of sodium dodecyl sulfate. Two dimensional electrophoresis revealed the presence of more than 20 polypeptides. By electron microscopy after negative staining with sodium phosphotungstate the proteasome preparation appeared as symmetrical ring-shaped particles. The enzyme exhibited chymotrypsin-like, trypsin-like and peptidyl-glutamyl-peptide hydrolase activities. In addition, the differential sensitivity of these activities to several compounds (aldehyde peptides, sodium dodecyl sulfate and polylysine) strongly support the multicatalytic nature of this enzyme. The structural and biochemical data obtained indicated that the 20 S proteasome isolated from wheat leaves exhibits the canonical characteristics of this conserved particle. (C) 1997 Elsevier Science Ireland Ltd.