Aliphatic amino acids - derivatives of carboxylic acids - are widely distributed 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 variety of aminocarboxylic amino acids in which the amino and carboxyl groups are bonded to an aliphatic carbon atom. The term "aliphatic" refers to linear or branched chains of atoms of a given element.
The bulk of the amino acids that have been isolated from living organisms are aliphatic. In chemistry, they mainly use the everyday names of these substances according to the original proteins from which they were obtained, since according to the systematic nomenclature they have too cumbersome names.
Types of connections by structure
Aliphatic amino acids, depending on the position of the amino and carboxyl groups, are divided into the following types:
- Alpha isomers. These include the bulk of natural compounds found in plants, microorganisms, and 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 β-alanine, which is part of coenzyme A. The latter is involved in the synthesis and oxidation of fatty acids.
- Gamma isomers. One of the brightest representatives of this group is ɣ-aminobutyric acid (GABA), the most important neurotransmitter of the nervous system responsible for the inhibition of nervous processes, the weakening and suppression of excitation.
All alpha-type amino acids, except for glycine, have an asymmetric structure, exist in the form of two mirror reflections that do not combine in space (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 proteins in ribosomes under the control of RNA. Themthe sequence is genetically encoded. There are only twenty such amino acids.
- Non-proteinogenic (non-coding), not part of proteins, but performing important functions (mainly participation in metabolic processes). Some of them are toxins and poisonous to humans.
According to acid-base properties, aliphatic amino acids are divided into 3 types:
- sour (aspartic and glutamic acids);
- neutral, containing the same number of basic and acidic groups;
- basic (histidine, arginine, lysine and others).
Physical and chemical characteristics
The following properties are typical for aliphatic amino acids:
- structure in the form of bipolar ions in the crystalline state;
- high melting point (α-amino acids do not have a clear value);
- good solubility in water and aqueous solutions of alkalis, acids;
- amphoteric;
- 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 s alts with alkalis, which dissolve well in water.
Mixtures of these substances with their sodium or potassium s alts are used to make buffer solutions used for chemical analysis.
Synthesis
BUnder laboratory conditions, the production of these compounds is a difficult task, since they are optically active, and in natural conditions their production occurs with the participation of enzymes. Therefore, only racemic amino acids, which are a mixture of optical isomers, are obtained chemically.
As a starting material, α-halocarboxylic acids are used, which, when reacted with ammonia, give aliphatic amino acids. There are other ways to obtain - from keto acids and their derivatives in the process of reductive amination, from malonic ester, aminoacetic acid (glycine). For the synthesis of amino acids on an industrial scale, microbiological technologies are used. With the help of genetic engineering, these substances are isolated from protein molecules produced by specially cultivated microorganisms.
Role in nature
Only in plants and microorganisms, more than 200 aliphatic amino acids have been identified, and in total there are over five hundred of them today. They are part of the antibacterial substances (such as penicillin) that microorganisms produce and also form the cell walls of most bacteria.
In the body of animals, these substances perform the following main functions:
- synthesis of proteins, enzymes, hormones, coenzymes and other important organic compounds;
- formation of biologically active amines (dopamine, norepinephrine, epinephrine, serotonin and others);
- participation in the transmission of nerve impulses and metabolic processes.
In human brain cells there is an active metabolism with the participation of amino acids, the concentration of which is 7 times higher than that in blood plasma.
Medical applications
The use of these compounds for medicinal purposes is based on their ability to participate in the exchange of nitrogenous 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 uses in therapeutic practice.
- Glutamic acid - CNS pathology, epilepsy, psychosis, 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.
- Aminalone is a neurotropic agent.
- Cysteine - for cataracts.
- Acetylcysteine - in diseases of the respiratory system as a mucolytic.
