Carboxypeptidase A

Carboxypeptidase A is an enzyme that plays a crucial role in the process of protein digestion. It is classified as an exopeptidase, meaning it cleaves amino acids from the end of a peptide chain. Specifically, carboxypeptidase A removes the terminal amino acid with a free carboxyl group from a peptide, resulting in the release of an amino acid.

Function

Carboxypeptidase A is primarily found in the pancreas and is secreted into the small intestine, where it aids in the breakdown of proteins into smaller peptides and amino acids. It specifically targets peptides with a free carboxyl group at the C-terminus. By removing the terminal amino acid, carboxypeptidase A helps to further break down proteins into their constituent amino acids, which can then be absorbed by the body for various physiological processes.

Structure

Carboxypeptidase A is a zinc-dependent enzyme, meaning it requires the presence of zinc ions for its catalytic activity. It consists of a single polypeptide chain folded into a compact structure. The active site of the enzyme contains a zinc ion coordinated by several amino acid residues, which are essential for its enzymatic function.

Mechanism of Action

The mechanism of action of carboxypeptidase A involves the binding of the substrate peptide to the active site of the enzyme. The zinc ion facilitates the nucleophilic attack of a water molecule on the carbonyl carbon of the peptide bond, resulting in the formation of a tetrahedral intermediate. This intermediate is then stabilized by the zinc ion and other amino acid residues in the active site. Finally, a proton transfer occurs, leading to the release of the terminal amino acid and the formation of a new peptide bond.

Importance

Carboxypeptidase A plays a crucial role in the digestion and absorption of dietary proteins. Without the activity of this enzyme, the breakdown of proteins into absorbable amino acids would be incomplete, leading to impaired nutrient absorption and potential nutritional deficiencies. Additionally, carboxypeptidase A is also involved in other physiological processes, such as the regulation of peptide hormones and the degradation of certain toxic peptides.

Clinical Significance

Deficiencies or abnormalities in carboxypeptidase A can lead to various medical conditions. For example, a deficiency in this enzyme can result in a condition known as carboxypeptidase A deficiency syndrome, characterized by impaired protein digestion and malabsorption. Furthermore, carboxypeptidase A has been implicated in certain diseases, such as cancer, where its dysregulation can contribute to tumor growth and metastasis.

See Also

• Protease
• Digestive Enzymes
• Peptide Bond
• Zinc Ion

References

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