Proteolisi

Proteolisi, or proteolysis, is the biochemical process by which proteins are broken down into smaller peptides or amino acids. This reaction is essential for numerous physiological functions, including digestion, cellular regulation, protein turnover, and degradation of damaged or misfolded proteins.

The reaction is typically catalysed by proteases, a diverse group of enzymes that cleave peptide bonds at specific sites. Proteases are classified according to their catalytic mechanism: serine proteases, cysteine proteases, aspartic proteases, metalloproteases, and threonine proteases are the most common subclasses. Each subclass uses a distinct amino acid residue or cofactor to activate a water molecule for hydrolysis of the peptide bond.

Proteolysis can occur extracellularly, as in the digestive tract where pancreatic enzymes such as trypsin and chymotrypsin break down dietary proteins, or intracellularly within organelles such as lysosomes, where cathepsins degrade endocytosed material. The ubiquitin–proteasome system is another key intracellular pathway, targeting proteins tagged with ubiquitin for rapid and selective degradation by the 26‑S proteasome.

Regulation of proteolysis is tightly controlled to prevent accidental degradation of functional proteins. Inhibitory proteins, compartmentalisation, and specific signalling pathways modulate protease activity. Dysregulation may lead to diseases ranging from chronic inflammation and neurodegeneration to cancers, where excessive protease activity can facilitate tumour invasion and metastasis.

In cell biology, proteolysis also serves as a means of activating or deactivating proteins through limited cleavage; for example, the activation of pro‑enzymes (zymogens) and the processing of neuropeptides highlight the functional versatility of this essential biological process.