Carboxypeptidase A: Difference between revisions
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==Structure== | ==Structure== | ||
Bovine CPA exists as a | Bovine CPA exists as a monomeric unit with [http://en.wikipedia.org/wiki/Molecular_symmetry C1 symmetry] in the pancreatic physiological environment. The single polypeptide chain of CPA contains a mixture of <scene name='69/694222/3cpasecondarystructure/2'>α-helices and β-sheets</scene>; the helices are shown in magenta whereas the β-sheets are displayed in yellow. A [http://en.wikibooks.org/wiki/Structural_Biochemistry/Chemical_Bonding/_Disulfide_bonds disulfide bond] connects the residues Cys138 and Cys161, which can be seen in yellow in the <scene name='69/694222/1cpx_default/3'>original rotating figure</scene>. | ||
Six different biologically active forms of the CPA monomeric unit exist. <scene name='69/694222/1cpxcleavageforms/2'>Three of these active forms</scene> are produced following the cleavage of amino acid residue segments from the initial [http://en.wikipedia.org/wiki/Zymogen zymogen], or proenzyme, by trypsin and chymotrypsin, which are also found in the pancreas. Cleavage by trypsin generates either the '''α-form''' (residues Ala1-Asn307) or the '''β-form''' (residues Ser3-Asn307). Chymotrypsin cleavage generates the '''γ-form''' (residues Asn8-Asn307). The α-form essentially is the protein without any additional residue cleavages. The Ala and Arg residues, shown in red and white respectively, are cleaved in the β-form. In addition to the red and white residues, the residues displayed in cyan are cleaved to give the γ-form. The <scene name='69/694222/3cpageneticforms/3'>other three active forms</scene> of CPA arise from [http://en.wikipedia.org/wiki/Genetic_variation genetic variation] in residues located at three separate positions on the polypeptide chain. The differences include the following: Ile/Val179, Ala/Glu228, and Val/Leu305.<ref name="CPA1" /> Each of the six biologically active monomeric units carry out the same function of hydrolyzing the C-terminal [http://en.wikipedia.org/wiki/Peptide_bond peptide bond] of a polypeptide substrate. | Six different biologically active forms of the CPA monomeric unit exist. <scene name='69/694222/1cpxcleavageforms/2'>Three of these active forms</scene> are produced following the cleavage of amino acid residue segments from the initial [http://en.wikipedia.org/wiki/Zymogen zymogen], or proenzyme, by trypsin and chymotrypsin, which are also found in the pancreas. Cleavage by trypsin generates either the '''α-form''' (residues Ala1-Asn307) or the '''β-form''' (residues Ser3-Asn307). Chymotrypsin cleavage generates the '''γ-form''' (residues Asn8-Asn307). The α-form essentially is the protein without any additional residue cleavages. The Ala and Arg residues, shown in red and white respectively, are cleaved in the β-form. In addition to the red and white residues, the residues displayed in cyan are cleaved to give the γ-form. The <scene name='69/694222/3cpageneticforms/3'>other three active forms</scene> of CPA arise from [http://en.wikipedia.org/wiki/Genetic_variation genetic variation] in residues located at three separate positions on the polypeptide chain. The differences include the following: Ile/Val179, Ala/Glu228, and Val/Leu305.<ref name="CPA1" /> Each of the six biologically active monomeric units carry out the same function of hydrolyzing the C-terminal [http://en.wikipedia.org/wiki/Peptide_bond peptide bond] of a polypeptide substrate. | ||