Amine Oxidase

Related Reading

Amine oxidases are enzymes widely distributed among living organisms. They catalyze the oxidative deamination of many biologically important amines with the formation of the corresponding aldehyde, hydrogen peroxide and ammonia according to the equation:

RCH₂CH₂+O₂+H₂O→RCHO+H₂O₂

Subclass

• Lysyl oxidase

Lysyl oxidase (LOX) is an enzyme encoded by the LOX gene in humans. It catalyzes the conversion of lysine molecules into highly reactive aldehydes, thereby forming cross-links in extracellular matrix proteins. Its inhibitory effect can cause bone hyperplasia, but at the same time, the upregulation of tumor cells may promote the metastasis of existing tumors, making them malignant and cancerous.

Figure 1. Structure of lysyl oxidase (LOX).

Functions

Lysyl oxidase is an extracellular copper-dependent enzyme that catalyzes the formation of aldehydes from lysine residues in collagen and elastin precursors. The importance of lysyl oxidase-derived cross-linking was determined by animal studies in which lysine oxidase was determined by nutritional copper deficiency or by adding a lysyl oxidase inhibitor β-amino group to the diet Propionitrile (BAPN) to inhibit. Lysyl oxidase has also proven to be essential for the development of the respiratory system and skin. Its deletion may lead to defects in the transforming growth factor beta superfamily of proteins, thereby controlling cell growth and differentiation.

• Primary-amine oxidase

Primary amine oxidase, also known as semicarbazide-sensitive amine oxidase (SSAO), is an enzyme named as primary amine: oxygen oxidoreductase (deamination). Like monoamine oxidase (MAO), SSAO can make Short-chain primary amines are deaminated, but they are not sensitive to MAO inhibitors. In addition to other hydrazine, hydroxylamine and propargylamine, semicarbazide also inhibits this enzyme. However, hydrazine is a weak inhibitor, and stronger inhibitors have been developed. SSAO exists in the smooth muscle of blood vessels and various other tissues. The physiological function of SSAO is not fully understood. It is recommended for blood vessel development, lipolysis regulation and detoxification. It can be used as an auxiliary MAO removal enzyme. However, the oxidation process produces harmful products, which may be related to atherosclerosis and blood vessel damage that cause diabetes. Elevated SSAO activity has been observed in cases of atherosclerosis,
diabetes, obesity, carotid plaque and varicose veins.

Figure 2. Structure of Primary-amine oxidase.

• Diamine oxidase

Diamine oxidase (DAO) is involved in the metabolism, oxidation and inactivation of histamine and other polyamines (such as putrescine or spermidine) in animals. The highest levels of DAO expression were observed in the digestive tract and placenta. In humans, certain subtype cells of the placenta, the extravillous trophoblast cells, express this enzyme and secrete it into the blood of pregnant women. Decreased levels of diamine oxidase in maternal blood during early pregnancy may be a sign of trophoblast-related pregnancy diseases such as preeclampsia. Usually, this enzyme does not exist in human blood circulation or is only very rare, but it is greatly increased in pregnant women, indicating that it has a protective effect on bad histamine. It is also secreted by eosinophils. If there is a shortage of diamine oxidase in the human body, it may appear in the form of allergies or histamine intolerance.

Reference

1. Mondovì B.; et al. Structure and function of amine oxidase. Advances in Experimental Medicine and Bioligy. 1982，148: 141–53.