Trypsin: Definition

Detailed Explanation

Trypsin is a serine protease produced by the pancreas as the inactive zymogen trypsinogen, which is activated in the small intestine by the brush-border enzyme enterokinase. Trypsin specifically cleaves peptide bonds on the carboxyl side of positively charged amino acids — lysine (Lys, K) and arginine (Arg, R). This specificity is determined by an aspartate residue (Asp189) at the bottom of the enzyme's binding pocket, which forms an electrostatic interaction with the positive charge on Lys/Arg side chains.

Trypsin is one of the three major pancreatic proteases (along with chymotrypsin and elastase) responsible for protein digestion. Together, they break dietary proteins into oligopeptides and free amino acids for absorption. Trypsin also activates the other pancreatic zymogens (chymotrypsinogen, proelastase, procarboxypeptidase), making it the master activator of the digestive protease cascade. Premature activation of trypsinogen within the pancreas (rather than the intestine) is a major mechanism of acute pancreatitis.

Beyond digestion, trypsin is one of the most widely used enzymes in biochemistry and proteomics. Tryptic digestion — treating a protein sample with trypsin to generate predictable peptide fragments — is the standard sample preparation method for mass spectrometry-based protein identification (bottom-up proteomics). Because trypsin cleaves predictably after Lys and Arg, the resulting peptides have convenient sizes (typically 6–20 residues) and favorable ionization properties for MS analysis.

Key Facts

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