Question

Which metal ion is present as cofactor is carboxypeptidase?

Answer 1

Hint: This metal ion also has other functions such as synthesis of DNA, production of Proteins and Amino acids. It is considered as one of the essential nutrients for our body and taken as supplements. Due to its presence, this carboxypeptidase is also known as metalloid carboxypeptidase. It forms coordination bonds with four amino acid residues. It helps in hydrolysing the COOH group of amino acids. This metal ion is wholly responsible for the catalytic activity of the enzyme.

Complete answer:
Carboxypeptidase is a protease enzyme which cleaves or hydrolyses at the C -terminal end of protein. This enzyme is present in all animals, plants and bacteria. The main function is to aid in digestion and protein maturation. There are many types of carboxypeptidase. They are classified based on different cofactors they have on the active site and affinity towards different substrate amino acids.
Zinc containing carboxypeptidase is also known as Carboxypeptidase A or Metallo carboxypeptidase. The structure of Carboxypeptidase A is made up of a single polypeptide chain of \[307\] amino acids and a zinc cofactor present at the heart of the active site. The zinc ion is in a tetrahedral geometry forming coordination bonds with side chains of two histidine residues and one glutamic acid residue. The fourth bond will be with the carboxyl end of the substrate amino acid during catalysis. The zinc cofactor is very important for the catalytic activity of the enzyme.

Correct answer is Zinc \[(Z{n^{2 + }})\]

Note:
Carboxypeptidase is secreted by pancreas in humans and are responsible for catabolism. They are secreted in inactive form and are activated by trypsin. Carboxypeptidase A has strong preference towards aromatic or branched amino acids such as tyrosine, phenylalanine etc. The activity of carboxypeptidase is crucial in the lack of which may cause anxiety, depression, weakness etc.