Transamination of amino acids is the process of intermolecular transfer from the starting substance of the amino group to the keto acid without the formation of ammonia. Let us consider in more detail the features of this reaction, as well as its biological meaning.
Discovery history
The amino acid transamination reaction was discovered by Soviet chemists Kritzman and Brainstein in 1927. Scientists have worked on the process of deamination of glutamic acid in muscle tissue and found that as pyruvic and glutamic acids are added to the homogenate of muscle tissue, alanine and α-ketoglutaric acid are formed. The uniqueness of the discovery was that the process was not accompanied by the formation of ammonia. During the experiments, they managed to find out that the transamination of amino acids is a reversible process.
When the reactions proceeded, specific enzymes were used as catalysts, which were called aminoferases (transmaminases).
Process Features
Amino acids involved in transamination can be monocarboxylic compounds. In laboratory studies, it was found that transaminationasparagine and glutamine with keto acids occurs in animal tissues.
Active participation in the transfer of the amino group takes pyridoxal phosphate, which is a coenzyme of transaminases. In the process of interaction, pyridoxamine phosphate is formed from it. Enzymes act as a catalyst for this process: oxidase, pyridoxaminase.
Reaction mechanism
Transamination of amino acids was explained by Soviet scientists Shemyakin and Braunstein. All transaminases have the coenzyme pyridoxal phosphate. The transmission reactions it accelerates are similar in mechanism. The process proceeds in two stages. First, pyridoxal phosphate takes a functional group from the amino acid, resulting in the formation of keto acid and pyridoxamine phosphate. At the second stage, it reacts with α-keto acid, pyridoxal phosphate, the corresponding keto acid, is formed as end products. In such interactions, pyridoxal phosphate is the carrier of the amino group.
Transamination of amino acids by this mechanism was confirmed by spectral analysis methods. Currently, there is new evidence for the presence of such a mechanism in living beings.
Value in exchange processes
What role does amino acid transamination play? The value of this process is quite large. These reactions are common in plants and microorganisms, in animal tissues due to their high resistance to chemical, physical,biological factors, absolute stereochemical specificity in relation to D- and L-amino acids.
The biological meaning of amino acid transamination has been analyzed by many scientists. It has become the subject of a detailed study in metabolic amino acid processes. In the course of the research, a hypothesis was put forward about the possibility of the process of transamination of amino acids using transdeamination. Euler discovered that in animal tissues only L-glutamic acid is deaminated from amino acids at a high rate, the process being catalyzed by glutamate dehydrogenase.
The processes of deamination and transamination of glutamic acid are reversible reactions.
Clinical significance
How is amino acid transamination used? The biological significance of this process lies in the possibility of conducting clinical trials. For example, the blood serum of a he althy person has 15 to 20 units of transaminases. In the case of organic tissue lesions, cell destruction is observed, which leads to the release of transaminases into the blood from the lesion.
In the case of myocardial infarction, literally after 3 hours, the level of aspartate aminotransferase increases to 500 units.
How is amino acid transamination used? Biochemistry involves a transaminase test, according to the results of which the patient is diagnosed, and effective methods of treating the identified disease are selected.
Special kits are used for diagnostic purposes in the clinic of diseaseschemicals for rapid detection of lactate dehydrogenase, creatine kinase, transaminase activity.
Hypertransaminasemia is observed in diseases of the kidneys, liver, pancreas, as well as in case of acute carbon tetrachloride poisoning.
Transamination and deamination of amino acids are used in modern diagnostics to detect acute liver infections. This is due to a sharp increase in alanine aminotransferase in some liver problems.
Transamination participants
Glutamic acid has a special role in this process. A wide distribution in plant and animal tissues, stereochemical specificity for amino acids, and catalytic activity have made transaminases a subject of study in research laboratories. All natural amino acids (except methionine) interact with α-ketoglutaric acid during transamination, resulting in the formation of keto- and glutamic acid. It undergoes deamination under the action of glutamate dehydrogenase.
Oxidative deamination options
There are direct and indirect types of this process. Direct deamination involves the use of a single enzyme as a catalyst; the reaction product is keto acid and ammonia. This process can proceed in an aerobic way, assuming the presence of oxygen, or in an anaerobic way (without oxygen molecules).
Features of oxidative deamination
D-oxidases of amino acids act as catalysts of the aerobic process, and oxidases of L-amino acids will act as coenzymes. These substances are present in the human body, but they show minimal activity.
Anaerobic variant of oxidative deamination is possible for glutamic acid, glutamate dehydrogenase acts as a catalyst. This enzyme is present in the mitochondria of all living organisms.
In indirect oxidative deamination, two stages are distinguished. First, the amino group is transferred from the original molecule to the keto compound, a new keto and amino acids are formed. Further, the ketoskeleton catabolizes in specific ways, participates in the tricarboxylic acid cycle and tissue respiration, the end products will be water and carbon dioxide. In case of starvation, the carbon skeleton of glucogenic amino acids will be used to form glucose molecules in gluconeogenesis.
The second stage involves the elimination of the amino group by deamination. In the human body, a similar process is possible only for glutamic acid. As a result of this interaction, α-ketoglutaric acid and ammonia are formed.
Conclusion
Determination of the activity of two enzymes of transamination of aspartate aminotransferase and alanine aminotransferase has found application in medicine. These enzymes can reversibly interact with α-ketoglutaric acid, transfer functional amino groups from amino acids to it,forming keto compounds and glutamic acid. Despite the fact that the activity of these enzymes increases in diseases of the heart muscle and liver, the maximum activity is found in the blood serum for AST, and for ALT in hepatitis.
Amino acids are indispensable in the synthesis of protein molecules, as well as the formation of many other active biological compounds that can regulate metabolic processes in the body: hormones, neurotransmitters. In addition, they are donors of nitrogen atoms in the synthesis of non-protein nitrogen-containing substances, including choline, creatine.
Ketabolism of amino acids can be used as an energy source for the synthesis of adenosine triphosphoric acid. The energy function of amino acids is of particular value in the process of starvation, as well as in diabetes mellitus. Amino acid metabolism allows you to establish links between numerous chemical transformations that occur in a living organism.
The human body contains about 35 grams of free amino acids, and their blood content is 3565 mg/dL. A large amount of them enters the body from food, in addition, they are in their own tissues, they can also be formed from carbohydrates.
In many cells (except erythrocytes) they are used not only for protein synthesis, but also for the formation of purine, pyrimidine nucleotides, biogenic amines, membrane phospholipids.
During the day, about 400 g of protein compounds break down into amino acids in the human body, and the reverse process occurs in approximately the same amount.
Fabricproteins are not able to carry out the costs of amino acids for the synthesis of other organic compounds in the case of catabolism.
In the process of evolution, humanity has lost the ability to synthesize many amino acids on its own, therefore, in order to provide the body with them in full, it is necessary to obtain these nitrogen-containing compounds from food. The chemical processes in which amino acids participate are still the subject of study by chemists and physicians.
