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Reactions of the carboxyl group

1. Decarboxylation of amino acids. Prosthetic group of L-amino acid decarboxylases is pyridoxal phosphate (the active form of vitamin B1). Amines are products of amino acids decarboxylation. Since they are formed as the metabolic products and possess high physiological activity they are called biogenic amines.

4 types of amino acid decarboxylation were founded. α-Decarboxylation is characteristic for animal tissues.

Decarboxylation of histidine leads to histamine formation. It causes vasodilatation in inflammation, is involved in the secretion of hydrochloric acid in the stomach, which is used in the clinic in the study of gastric secretory activity (histamine test). With high sensitivity to histamine antihistamines are used.

Decarboxylation of glutamic acid leads to g-aminobutyric acid (GABA) formation:

ÍÎÎÑCH(NH2)CH2CH2COOH NH2CH2CH2CH2COOH + ÑÎ2

glutamic acid g- aminobutyric acid

 

It accumulates in the brain tissue and is the neurohumoral inhibitor. GABA is used in the clinic as a medicine for certain diseases of the CNS.

Decarboxylase of aromatic amino acids catalyzes decarboxylation of 3,4-dihydroxyphenylalanine (DOPA). Dopamine is produced. It is a precursor of adrenaline (epinephrine) and noradrenaline (norepinephrine).

The accumulation of biogenic amines can cause violations of some functions in the body. There are special mechanisms of neutralization of biogenic amines. There is their oxidative deamination with the formation of aldehydes and ammonia. Enzymes are monoamine oxidases and di-amine oxidases. The process is irreversible and proceeds in two stages:

 

Hydrogen peroxide then splits into water and oxygen. Monoamine oxidase (MAO), FAD-containing enzyme, is localized primarily in the mitochondria.

 


Date: 2016-04-22; view: 744


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