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chymotrypsin
Chymotrypsin (, ''chymotrypsins A and B'', ''alpha-chymar ophth'', ''avazyme'', ''chymar'', ''chymotest'', ''enzeon'', ''quimar'', ''quimotrase'', ''alpha-chymar'', ''alpha-chymotrypsin A'', ''alpha-chymotrypsin'') is a digestive enzyme component of pancreatic juice acting in the duodenum where it performs proteolysis, the breakdown of proteins and polypeptides. Chymotrypsin preferentially cleaves peptide amide bonds where the carboxyl side of the amide bond (the P1 position) is a large hydrophobic amino acid (tyrosine, tryptophan, and phenylalanine). These amino acids contain an aromatic ring in their sidechain that fits into a 'hydrophobic pocket' (the S1 position) of the enzyme. It is activated in the presence of trypsin. The hydrophobic and shape complementarity between the peptide substrate P1 sidechain and the enzyme S1 binding cavity accounts for the substrate specificity of this enzyme. Chymotrypsin also hydrolyzes other amide bonds in peptides at slower rates, particularly those containing leucine and methionine at the P1 position.
Structurally, it is the archetypal structure for its superfamily, the PA clan of proteases.
== Activation ==
Chymotrypsin is synthesized in the pancreas by protein biosynthesis as a precursor called chymotrypsinogen that is enzymatically inactive. On cleavage by trypsin into two parts that are still connected via an S-S bond, cleaved chymotrypsinogen molecules can activate each other by removing two small peptides in a ''trans''-proteolysis. The resulting molecule is active chymotrypsin, a three-polypeptide molecule interconnected via disulfide bonds.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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