CHARACTERIZATION OF PROTEASOMES ISOLATED FROM RAT-LIVER

Proteasomes are cylindrical particles which have a pseudo-helical arra ngement of subunits. On 2D-PAGE gels, rat liver proteasome preparation s give rise to up to 25 proteins which are encoded by at least 16 diff erent genes that are all members of the same family. Proteasomes are a ble to degrade protein substrates to acid soluble peptides. They have at least five different catalytic components which can be distinguishe d by the use of synthetic peptide substrates and inhibitors which have very different reactivity at the different sites. Proteasomes can und ergo conformational changes when treated with various effecters of the ir multiple peptidase activities. They are found in the nucleus and in the cytoplasm and, in cultured cells, show changes in localization du ring the course of the cell cycle.