Characterization of proteasomes isolated from rat liver.

Proteasomes are cylindrical particles which have a pseudohelical arrangement of subunits. On 2D-PAGE gels, rat liver proteasome preparations give rise to up to 25 proteins which are encoded by at least 16 different genes that are all members of the same family. Proteasomes are able to degrade protein substrates to acid soluble peptides. They have at least five different catalytic components which can be distinguished by the use of synthetic peptide substrates and inhibitors which have very different reactivity at the different sites. Proteasomes can undergo conformational changes when treated with various effectors of their multiple peptidase activities. They are found in the nucleus and in the cytoplasm and, in cultured cells, show changes in localization during the course of the cell cycle.