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is a display of carboxypeptidase A without the substrate.
This enzyme is found in the pancreas where it catalyzes the hydrolysis
of C-terminal amino acid residues of peptides, proteins and related
PeptideCO-NHCH(R)COOH + H2O
PeptideCOOH + NH2CH(R)COOH
It shows a preference for substrates (amino acids) with aromatic side chains such as phenylalanine, tryptophan and tyrosine. Carboxypeptidase has a zinc(II) ion in its active site and was one of the first zinc enzymes to be discovered.
10 electronic configuration.
2O shown as just the oxygen atom (red).
2+. One glutamate oxygen and nitrogen from His196 occupy the axial, while the other glutamate oxygen, water oxygen and nitrogen on His69 occupy the equatorial positions. Click
2+ and assisted by a Glu 270. The combination of the zinc ion and the neighbouring positively charged residues lower the pKa of the water to approximately 7. A secondary purpose for Zn2+ along with Arg 127, Arg 145 and Tyr 248 is to stabilize the negatively charged intermediates formed during hydrolysis. Here a negatively charged lactate ion (ball and stick) is held in the substrate binding site. This models the amino acid (the leaving group), which is cleaved from the end of the peptide chain where the O of lactate would really be an NH2.
To see a more detailed schematic presentation of the mechanism click here.
2+ centre accessible to other, 2e- donor ligands. The model complex shown on the left contains a
- group from glutamate residues respectively . The drawback of this ligand is the fact that it can bridge between Zn(II) centres forming a chain structure in the solid state. The existence of two different carbonyl stretching frequencies (at 1668 and 1642 cm-1) in the solution IR spectrum of the complex suggests that the solution contains a mixture of monomeric and polymeric species. Even though this compound resembles the active site of the enzyme, it is not able to assist in peptide bond cleavage.
To learn about simple complexes capable of catalytic hydrolysis of peptide bonds see Chin, Jik (1991) Acc. Chem. Res. 24, 145.