In a cell, protein degradation and synthesis maintain the balance of proteins, where old proteins are degraded into amino acids, which are further used in the synthesis of new proteins. Proteases/Peptidases play an important role in protein degradation. Proteases are present in almost all living cells. In a living cell, protease action is regulated by external as well as internal factors. Some proteases are inactive under normal conditions, but are activated only when necessary. For example, during apoptosis, Pro-caspase (inactive) converts to Caspase (active). Sub-cellular localization of proteases also helps in their regulated activity. Most of them are localized to sub-cellular organelles like lysosomes and thereby restricted their activity only to those proteins directed to lysosomes.
