Aliphatic amino acids - derivatives of carboxylic acids - are widespread in nature. They play an important role in many vital processes. On their basis, some types of medicines are made.
Aliphatic amino acid - what is it?
Amino acids perform important functions in the human body and other animals, as they are neurotransmitters and "building blocks" for building proteins. They are also needed for proper metabolism.
Aliphatic amino acids are a type of aminocarboxylic amino acids in which the amino and carboxyl groups are linked to an aliphatic carbon atom. The term "aliphatic" means a linear or branched chain of atoms of a given element.
The bulk of the amino acids that have been isolated from living organisms are specifically aliphatic. In chemistry, they use mainly the common names of these substances according to the source proteins from which they were obtained, since according to the systematic nomenclature they have too bulky names.
Types of compounds by structure
Aliphatic amino acids, depending on the position of amino and carboxyl groups, are divided into the following types:
Alpha isomers. These include the bulk of natural compounds that are found in plants, microorganisms, animals. They are also found in meteorites, and the structure of these substances is the same as that of terrestrial living beings.
Betta amino acids. An example is ฮฒ-alanine, which serves as part of coenzyme A. The latter is involved in the synthesis and oxidation of fatty acids.
Gamma isomers. One of the prominent representatives of this group is ษฃ-aminobutyric acid (GABA), the most important neurotransmitter of the nervous system, responsible for inhibiting the nervous processes, weakening and suppressing excitation.
All alpha-type amino acids, except glycine, have an asymmetric structure, exist in the form of two specular, space-incompatible reflections (L- and D-amino acids) and have natural optical activity. The most important L-amino acids are glycine, alanine, serine, cysteine, aspartic acid, tyrosine, leucine, glutamine, isoleucine, arginine, lysine, proline.
Examples of aliphatic amino acids are shown in the figure below.
Types of substances according to other criteria
There is also a classification according to the nature of the participation of aliphatic amino acids in protein synthesis.
Proteinogenic compounds from the L-series, which are attached to the composition of proteins in ribosomes under the control of RNA. Their sequence is genetically encoded. There are only twenty such amino acids.
Non-proteinogenic (non-encoded), not included in the composition of proteins, but performing important functions (mainly, participation in metabolic processes). Some of them are toxins and toxic to humans.
According to acid-base properties, aliphatic amino acids are divided into 3 types:
acidic (aspartic and glutamic acids);
neutral, containing the same number of basic and acid groups;
the main ones (histidine, arginine, lysine and others).
Physicochemical Characteristics
Aliphatic amino acids are characterized by the following properties:
structure in the form of bipolar ions in a crystalline state;
high melting point (ฮฑ-amino acids do not have a clear value);
good solubility in water and aqueous solutions of alkalis, acids;
amphotericity;
basic properties in an acidic environment and vice versa;
if the pH of the medium is greater than the isoelectric point, then aliphatic amino acids form salts with alkalis that dissolve well in water.
From mixtures of these substances with their sodium or potassium salts make buffer solutions used for chemical analysis.
Synthesis
In laboratory conditions, the production of these compounds is a difficult task, since they are optically active, and in vivo their production occurs with the participation of enzymes. Therefore, only racemic amino acids, which are a mixture of optical isomers, are chemically produced.
The starting material used is ฮฑ-halocarboxylic acids, which, when reacted with ammonia, produce aliphatic amino acids. There are other methods of preparation - from keto acids and their derivatives in the process of reductive amination, from malonic ester, aminoacetic acid (glycine). Microbiological technologies are used for the synthesis of amino acids on an industrial scale. Using genetic engineering, these substances are isolated from protein molecules produced by specially cultivated microorganisms.
Role in nature
In plants and microorganisms alone, more than 200 aliphatic amino acids have been identified, and in total there are over five hundred to date. They are part of antibacterial substances (for example, penicillin), which produce microorganisms, and also form the cell walls of most bacteria.
In animals, these substances perform the following main functions:
synthesis of proteins, enzymes, hormones, coenzymes and other important organic compounds;
the formation of biologically active amines (dopamine, norepinephrine, adrenaline, serotonin and others);
participation in the transmission of nerve impulses and in metabolic processes.
In the cells of the human brain, an active metabolism occurs with the participation of amino acids, the concentration of which exceeds 7 times that in the blood plasma.
Medical use
The use of these compounds for therapeutic purposes is based on their property to participate in the exchange of nitrogen elements and the synthesis of biologically active substances. There are many drugs that contain aliphatic amino acids. Listed below are some of them and their purpose in therapeutic practice.
Glutamic acid - CNS pathologies, epilepsy, psychoses, mental retardation in children, cerebral palsy, Down's disease.
Methionine - toxic liver damage (cirrhosis, poisoning with arsenic, chloroform and other toxins), as well as diseases of this organ in chronic alcoholism, diabetes mellitus.
Aminalon is a neurotropic agent.
Cysteine โโ- with cataracts.
Acetylcysteine โโ- for respiratory diseases as a mucolytic.