Definition
Carboxypeptidases are enzymes that cleave amino acids from proteins or peptides. Proteins are long chains consisting of different amino acids. Peptides also consist of amino acids, but are shorter.
The basic structure of amino acids is always the same. It is important that the connection between a carbon atom and a nitrogen atom is established. Figuratively speaking, one can imagine this as a human chain, the right hand is the carbon atom and the left hand is the nitrogen atom.
So at the ends of the chain one of the atoms remains free at each end. Carboxypeptidases cleave off the last amino acid at the end of the proteins where the carbon atom remains free. It is called the so-called C-terminal end. Since the enzyme can only cleave at the ends, it is referred to as an exopeptidase. Carboxypeptidases are on the one hand involved in the splitting of the ingested food, on the other hand they also modify newly produced proteins and bring them into their functional state.
What carboxypeptidases are there?
Carboxypeptidases can be subdivided according to different systems. One system divides the carboxypeptidases according to which amino acids they preferentially cleave. In this system, the carboxypeptidases are divided into several groups that are designated by letters.
The best known groups are groups A and B. The carboxypeptidases of group A split off the amino acids that have a branched structure and those that have an aromatic ring. This ring is a special structure consisting of carbon atoms and has special properties.
The carboxypeptidases of group B preferentially cleave off amino acids which are positively charged. The other system for the classification of carboxypeptidases divides the enzymes according to the type of their active centre. The active centre refers to the site of the enzyme where the reaction takes place.
In carboxypeptidases, a distinction is made between metallo-carboxypeptidases, in which a metal molecule is located in the active centre, thiol-carboxypeptidases, with the amino acid cysteine in the active centre, and serine carboxypeptidases, in which the amino acid serine is located in the active centre. However, the different active centres do not determine which amino acid is cleaved off. The class of serine carboxypeptidases consists of three enzymes: trypsin, chymotrypsin, elastase.
Task, function and effect
The tasks of the different carboxypeptidases are very diverse. While the carboxypeptidases that were first discovered play a role in digestion, most carboxypeptidases known today are important for other processes. The task of carboxypeptidases in digestion is to break down proteins into their individual amino acids.
This process is very important because the intestine does not absorb proteins, only the individual amino acids. Carboxypeptidases are indispensable in the maturation process of various proteins. In order for proteins to become fully functional after their production, various modifications have to be made.
For example, individual amino acids are split off by the carboxypeptidases. However, this modification is not only carried out by carboxypeptidases but also in interaction with other enzymes. Furthermore, carboxypeptidases are involved in the production of different peptides. A particularly important peptide is insulin. Various carboxypeptidases are also involved in the production of insulin.