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The main substrates of chymotrypsin are peptide bonds in which the amino acid N-terminal to the bond is a tryptophan, tyrosine, phenylalanine, or leucine. Like many proteases, chymotrypsin also hydrolyses amide bonds in vitro, a virtue that enabled the use of substrate analogs such as N-acetyl-L-phenylalanine p-nitrophenyl amide for enzyme assays.
The active form is called π-chymotrypsin and is used to create α-chymotrypsin. Trypsin cleaves the peptide bond in chymotrypsinogen between arginine-15 and isoleucine-16. This creates two peptides within the π-chymotrypsin molecule, held together by a disulfide bond. One π-chymotrypsin acts on another by breaking a leucine and serine ...
The triad is a coordinated structure consisting of three amino acids: His 57, Ser 195 (hence the name "serine protease") and Asp 102. These three key amino acids each play an essential role in the cleaving ability of the proteases.
Different enzymes have different specificity for their substrate; trypsin, for example, cleaves the peptide bond after a positively charged residue (arginine and lysine); chymotrypsin cleaves the bond after an aromatic residue (phenylalanine, tyrosine, and tryptophan); elastase cleaves the bond after a small non-polar residue such as alanine or ...
They are usually very specific for certain amino acids. Examples of endopeptidases include: Trypsin - cuts after Arg or Lys, unless followed by Pro. Very strict. Works best at pH 8. Chymotrypsin - cuts after Phe, Trp, or Tyr, unless followed by Pro. Cuts more slowly after His, Met or Leu.
Chymotrypsin is weaker at digesting elastin than the architypical pancreatic elastase. [ 4 ] Some bacteria (including Pseudomonas aeruginosa ) also produce elastase; bacterial elestases work in many ways and include serine proteases , aspartic proteases , thiol proteases , and metalloenzymes .
Chymotrypsin preferentially cleaves C-terminally of large aromatic residues such as phenylalanine (left). The peptide backbone is colored dark red, the sidechains are shown in bright red. In the first step, the catalytic triade enhances the nucleophilicity of Ser 195 which attacks the carbon atom of the peptide bond, leading to formation of a ...
The triad typically consists of cysteine, histidine, and aspartate amino acids, where the cysteine acts as a nucleophile, the histidine acts as a chemical base, and the aspartate stabilizes the histidine. [11] Examples of cysteine aminopeptidases include cathepsin H and aminopeptidase B. [8]