Apoperoxidase

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Apoperoxidase is a type of oxidoreductase produced by microorganisms or plants. They can catalyze many reactions. Apoperoxidase is an enzyme that uses hydrogen peroxide as an electron acceptor to catalyze the oxidation of a substrate. Mainly exists in the peroxisome of the carrier, with iron porphyrin as the auxiliary group, it can catalyze hydrogen peroxide, oxidize phenol and amine compounds and hydrocarbon oxidation products, which has the dual effect of eliminating the toxicity of hydrogen peroxide and phenols, amines, aldehydes and benzene.

Figure 1. Protein structure of ApoApoperoxidase.

Introductions

Apoperoxidase is a kind of oxidoreductase. Distributed in breast milk, white blood cells, platelets and other body fluids or cells, the prosthetic group of the enzyme is also heme, the enzyme that uses H₂O₂ as the electron acceptor to catalyze the oxidation of the substrate, it catalyzes the direct oxidation of phenolic or amine compounds by H₂O₂, such as cereals Glutathione apoperoxidase, eosinophil apoperoxidase and thyroid apoperoxidase, etc., have the dual effect of eliminating the toxicity of hydrogen peroxide and phenolic amines. The reaction is as follows: R+ H₂O₂RO+H₂O or RH₂+ In the clinical diagnosis of H₂O₂-R+2H2O, to observe whether there is occult blood in the stool is to use the activity of apoperoxidase in red blood cells to oxidize benzidine into a blue compound.

Enzyme

Peroxisomes are vesicles wrapped by a unit membrane, with a diameter of about 0.5 to 1.0μm, usually smaller than mitochondria. It is ubiquitous in various types of eukaryotic cells, especially in hepatocytes and kidney cells. The marker enzyme of peroxisome is catalase, and its main function is to hydrolyze hydrogen peroxide. Hydrogen peroxide (H₂O₂) is a cytotoxic substance produced in the redox reaction catalyzed by oxidase. Both oxidase and catalase are present in peroxisomes, thereby protecting cells.

Morphology

Peroxisome is also called microbody. When peroxisome was discovered in 1954, because the function of this particle was unknown, it was called microbody. Peroxisomes are different from lysosomes. Peroxisomes do not come from the endoplasmic reticulum and Golgi apparatus, so it is not a membrane-bound organelle of the inner membrane system. Peroxisomes are commonly found in various types of eukaryotic cells, but they are particularly abundant in liver cells and kidney cells. Peroxisomes are rich in enzymes, mainly oxidase, catalase and apoperoxidase. Oxidase can act on different substrates, and its common feature is that it reduces oxygen to hydrogen peroxide while oxidizing the substrate. The marker enzyme of peroxisome is catalase, and its main function is to hydrolyze hydrogen peroxide (H₂O₂, Hydrogen Peroxide). Oxidase and catalase are both present in peroxisomes, which protect cells.

Functions

• Inactivate toxic substances

This effect is that catalase uses hydrogen peroxide to oxidize various substrates, such as phenol, formic acid, formaldehyde, and ethanol. As a result of oxidation, these toxic substances become non-toxic substances, which can effectively decompose formaldehyde and toluene. At the same time, H₂O₂ is further transformed into non-toxic H2O. This detoxification effect is particularly important for the liver and kidneys. For example, almost half of the ethanol that people drink is oxidized into acetaldehyde in this way, thereby removing the toxic effect of ethanol on cells.

• Regulating effect on oxygen concentration

Peroxisomes and mitochondria have different sensitivity to oxygen. The optimal oxygen concentration required for mitochondrial oxidation is about 2%. Increasing the oxygen concentration does not improve the mitochondrial oxidation capacity. The oxidation rate of peroxisomes increases in proportion to the increase in oxygen tension. Therefore, under the condition of low concentration of oxygen, the ability of mitochondria to utilize oxygen is stronger than that of peroxisome, but under the condition of high concentration of oxygen, the oxidation reaction of peroxisome is dominant. This characteristic makes peroxidation Enzymes have the toxic effect of protecting cells from high concentrations of oxygen.

• Fatty acid oxidation

About 25-50% of fatty acids in animal tissues are oxidized in peroxisomes, and the rest are oxidized in mitochondria. In addition, since there are enzymes related to phospholipid synthesis in peroxisomes, peroxisomes are also involved in lipid synthesis.

• Metabolism of nitrogenous substances

In most animal cells, urate oxidase is necessary for the oxidation of uric acid. Uric acid is a product of degradation and metabolism of nucleotides and certain proteins. Uric acid oxidase can further oxidize and remove this metabolic waste. In addition, peroxisomes are also involved in other nitrogen metabolism, such as aminotransferase (aminotransferase) catalyzes the transfer of amino groups.

Application

For example, catalase is a kind of apoperoxidase. Catalase can be used in conjunction with glucose oxidase to remove the glucose in the egg white and replace the traditional natural fermentation method, thereby improving product quality and shortening the production cycle. In medicine, it can also be used as a tool enzyme to test urine sugar and blood sugar. Modern medicine believes that the body's aging is related to oxidation, such as the oxidation of chromosomes and enzymes. Therefore, some substances with reducing functions can be anti-aging to some extent, such as peroxisomes, vitamin C and E also have anti-aging effects.

References

1. Skeggs LT.; et al. The preparation and function of the hypertensin-converting enzyme. The Journal of Experimental Medicine. 1956, 103 (3): 295–9.
2. Natesh R.; et al. Crystal structure of the human angiotensin-converting enzyme-lisinopril complex. Nature. 2003, 421 (6922): 551–4.