The proteolytic enzymes are responsible for a variety of vital biological and pathological processes that include degradation and/or processing of key regulatory proteins during metabolic turnover and activation of transcription factors by removing the inhibitory elements. These proteases function in the post-translational modification of proteins that influence their rate of degradation. Protein degradation that plays an important role in the control and regulation of many crucial biological functions, ranging from cell cycle progression to presentation of viral antigens for scrutiny by cells of the immune system, is mediated by lysosomal and nonlysosomal proteolytic pathways. Among the nonlysosomal system, Multicatalytic Proteinase Complex (MPC) also known as Proteasome represents a very important class. These enzymes are large multi-subunit protease complexes that are localized in the nuclear and cytosol compartments of eukaryotic cells. They contain a number of peptidase and protease activities within the same macromolecule, each with a specific task of degradation of both ubiquitin and non-ubiquitin-conjugated proteins. They are implicated in the degradation of proteins involved in cell cycle traverse, proliferation, Alzheimer`s disease, programmed cell death or apoptosis and in a diverse set of processes including antigen presentation and selective intracellular proteolysis event. Current evidence indicates that MFC`s are involved in multiple peptidase activities that are expressed via ubiquitin-independent pathways through 20S complex or via ubiquitin-dependent proteolytic pathways through 26S complex. These enzymes also play important contribution in the field of food science (particularly livestock) and agriculture chemistry. In this review, a short summary is presented on the structural, biochemical mechanisms, physiological functions and enzymological description of MPC with a special relevance to human pathologies. The various types of proteolytic activities exhibited by MPC including their potential substrates, the method of assay of individual activity, their specific inhibitors and possible applications as therapeutic agents are discussed.
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