Carboxypeptidase A: Difference between revisions

Bovine CPA exists as a single unit with [http://en.wikipedia.org/wiki/Molecular_symmetry C1 symmetry] in the pancreatic physiological environment.  The single polypeptide chain contains a mixture of <scene name='69/694222/3cpasecondarystructure/1'>α-helices and β-sheets</scene>, of which there are a total of 11 helices (one 3₁₀, eight 3.6₁₃) and ten β-strands.  The helices are shown in magenta, and the β-strands are displayed in yellow.

Six different biological active forms of the monomeric CPA unit exist.  Three of these active forms are produced following the cleavage of amino acid residue segments from the initial zymogen, or proenzyme, by trypsin and chymotrypsin, which are also found in the pancreas.  Cleavage by trypsin generates either the alpha-form (residues Ala1-Asn307) or the beta-form (residues Ser3-Asn307).  Chymotrypsin cleavage generates the gamma-form (residues Ser3-Asn307).  The other three active forms of CPA arise from genetic variation in residues located in three separate positions of the polypeptide chain.  The differences include the following: Ile/Val179, Ala/Glu228, and Val/Leu305.  Each of the six biologically active monomeric units carry out the same function of hydrolyzing the C-terminal peptide bond of a polypeptide substrate.