(Science: cell biology) proteolytic complexes that degrade cytosolic and nuclear proteins. Implicated in aTP dependent ubiquitin protein complex degradation and in antigen processing in antigen presenting cells. The 20S proteasome (700 kD), essential in ATP ubiquitin degradation pathway, has 13-15 subunits each of which has three or four different peptidase activities. 26S proteasomes may be formed in an ATP dependent fashion from a 20S proteasome and additional components, CF1 (660 kD), CF2 (250 kD) and CF3 (600 kD).
Origin: Gr. Soma = body