Aminopeptidase

Related Reading

Aminopeptidase is a type of exoprotease that can selectively cleave amino acid residues from the N-terminus of proteins and polypeptides to produce free amino acids. Proteases can be divided into two categories according to the different sites of action: endoproteases and exoproteases. Exoproteases can be divided into aminopeptidases and carboxypeptidases.

Figure 1. Protein structure of aminopeptidase.

Classifications

There are many kinds of aminopeptidase, and classifying aminopeptidase according to different characteristics is very helpful for people to know and understand aminopeptidase. There are many ways to classify aminopeptidases, such as by substrate specificity, by location in the cell, by catalytic properties, by optimal pH, etc. The following three main classification methods are introduced:

(1) According to the different substrate specificity of aminopeptidase, aminopeptidase is divided into two categories: one is aminopeptidase with strict substrate specificity, they can only specifically hydrolyze one or one Similar to amino acids, another type of aminopeptidase has a wider substrate spectrum and can hydrolyze most amino acids. This type of aminopeptidase is generally named according to their most suitable reaction substrate.

(2) According to the different catalytic methods of aminopeptidase, aminopeptidase can be divided into three categories: metallo, cysteine, and serine aminopeptidase. Most reported aminopeptidases are metalloaminopeptidases, accounting for about 70% of the total.

(3) According to the optimal pH of aminopeptidase, aminopeptidase can be divided into three categories: acidic, neutral and alkaline aminopeptidase. Generally, we call acid aminopeptidase with the optimum pH of 2.0-6.0, neutral aminopeptidase with pH 6-8, and alkaline aminopeptidase with pH above 8.5. Most of the aminopeptidases derived from bacteria are alkaline aminopeptidases. The optimal reaction pH of aminopeptidase is generally 6-9, and only a few aminopeptidase are not in this range.

(4) Depending on the location of aminopeptidase in the cell, some aminopeptidase exists in the cytoplasm, some aminopeptidase exists on the cell wall of some Gram-positive bacteria, and a small part of aminopeptidase can interact with Membrane bonding.

Source

As a kind of protease, aminopeptidase is widely present in different species of organisms, including mammals, plants, microorganisms, etc. In animals, Japanese scholar Akihiro okitani isolated a proteolytic enzyme with aminopeptidase activity from rabbit skeletal muscle for the first time and named it "BANA hydrolase H". Prior to this, Chinese scholar Mei Chuansheng et al. reported for the first time a plant-derived aminopeptidase and studied the changes of this enzyme during the senescence of rice leaves. With the in-depth research on aminopeptidases, more and more aminopeptidases from plants and animals have been reported.

Application

• Used to remove the bitter taste of protein hydrolysate

When protein macromolecules are enzymatically digested, the hydrophobic amino acids contained in the peptide chain are exposed, touch the taste buds and produce a bitter taste. Therefore, the protein hydrolysate after protease hydrolysis usually exhibits a bitter taste. Studies have reported that the use of aminopeptidase to further hydrolyze the protein enzymatic solution can remove its bitter taste.

• Deep hydrolysis of protein

Combined with protease, it can greatly increase the degree of protein hydrolysis. In the process of soy sauce brewing, cheese production and other protein hydrolyzed products, the utilization rate of protein can be improved and the cost can be saved. For example, Cui Chun and Zhao Mouming used flavor protease (a complex of protease and aminopeptidase) to deep enzymatically hydrolyze blue garden fish ginseng protein. After 6 hours of enzymatic hydrolysis, the protein utilization rate reached 83.3%, and the degree of hydrolysis reached 59.7% at 21 hours.

• Preparation of biologically active peptides

Most of the biologically active peptides are cell growth factors. Their content in the body is extremely low, but their biological activity is extremely high, and they play a biological regulatory role in a variety of cell physiological functions and metabolic activities. It has the functions of health care and beauty. Obtaining specific active peptides by controlling the enzymatic hydrolysis of proteins is a safe and efficient way to prepare active peptides. Liu Communication and others first hydrolyzed soybean protein isolate with protease, and then hydrolyzed it with aminopeptidase. The study found that the content of peptides in the product can be increased by about 12% compared with that of protease hydrolysis alone.

• Special use in medicine

Prolinase can effectively remove neurotoxic chemical agents and organophosphorus pesticides, and can be used as a medical antidote as well as an environmental disinfectant. Leucyl aminopeptidase can also be used as a molecular tool for protein sequence determination.

References

1. Karmen A.; et al. Transaminase activity in human blood. The Journal of Clinical Investigation. 1955, 34 (1): 126–31.
2. Giannini EG.; et al.. Liver enzyme Aminopeptidaseeration: a guide for clinicians. Canadian Medical Association Journal. 2005, 172 (3): 367–79.