Generality
Transaminases are enzymes that intervene in transamination, ie in the transformation of one amino acid into another; therefore they also participate in the transformation of amino acids into energy, especially if we are faced with a long and demanding physical effort.
Transaminases, more precisely, catalyze transfer reactions of an amino group (-NH 2 ) from a donor amino acid (usually glutamate) to an α-keto acid acceptor. They also contain a vitamin coenzyme, pyridoxal phosphate (Vit. B6) (PLP), which during the reaction receives the amino group from glutamate and becomes pyridoxamine phosphate (PMP).
When the hepatic cells ( hepatocytes ) or those of the muscles ( myocytes ) are damaged and break down, the transaminases escape and flow into the blood, increasing their concentration.
In detail, transaminases are:
- glutamic-oxaloacetic acid ( GOT or AST, aspartate-aminotransferase, present in muscles and myocardium);
- glutamic-pyruvic acid ( GPT or ALT, alanine-aminotransferase, present in liver cells);
however, other enzymes similar to transaminases also exist and are all indices of severe hepatocellular necrosis, as well as of other organs. These are:
- lactic dehydrogenase ( LDH );
- gamma-glutamyl transpeptidase ( Gamma-Gt );
- alkaline phosphatase ( FA );
- ornithyl carbamyl transferase ( OCT );
- aldolase.
Thanks to transaminases, doctors have a group of specific tests available to assess the functional status and, even within certain limits, anatomy of the hepatocytes. These tests express the state of permeability of cell membranes: if hepatocytes suffer, the membrane of these cells is no longer able to perform the normal barrier functions, so it is more permeable than normally. Of course, this abnormal permeability is especially relevant in the presence of necrosis (death) of hepatocytes, when these cells discharge all their contents outside.
These tests are very sensitive and highlight even small functional changes of hepatocytes in which there is a state of suffering of the cell membrane; if they are altered in a high way, they indicate, instead, the existence of a necrotic process.
What's this
Transaminases (also known as aminotransferases) are enzymes involved in amino acid metabolism and glucose synthesis (neoglucogenesis).
It is a rather large group of molecules, but the type of reaction in which they are involved is always the same: the transfer of the amino portion (the one containing nitrogen) from an amino acid to an acid molecule (called alpha-keto acid) to transform it into another amino acid.
From the clinical point of view, the two most important transaminases are aspartate transaminase (AST or GOT) and alanine transaminase (ALT or GPT).
Deepening: What are enzymes
Enzymes are the largest and most highly specialized class of protein molecules. They catalyze (that is, they accelerate) the speed of the thousands of chemical reactions that together form the metabolism of the cells. In fact, almost all the chemical reactions that take place in the body, without the presence of enzymes, would happen too slowly to have biological value.
So, in other words, enzymes are biocatalysts, that is, they have the property of accelerating the speed of chemical reactions without appearing among the products of the reaction, that is, in the end they are found in the same conditions and in the same quantity they were at the beginning. of the reaction.
The enzymes act in very small quantities, not proportional to the entity of the reaction they catalyze. Furthermore, at the end of the reaction, they can be used again, ie they are not consumed.
Enzymes act only on the speed of the reaction. Furthermore, they are highly specific, so that there is a different enzyme for each biological reaction. This aspect is dictated by the fact that the activity of an enzyme can be carried out only if it binds to its substrate (the substance that reacts by the action of the enzyme); at the time of binding, the substrate is in activation conditions and reacts easily.
Because they measure themselves
The determination of transaminase levels in the blood is useful for assessing proper liver function, but also the state of health of the heart and the musculoskeletal system.
The dosage of transaminases is used both as a preventive measure (general monitoring), and when the doctor suspects a malfunction or injury of these organs.
Normal values
Transaminases, like all enzymes, are expressed in International Units, meaning the amount of enzyme that transforms one micromole of the substrate in one minute.
In the presence of acute or chronic liver disease, the increase in concentrations of different enzymes can be detected in the blood, in particular:
- GOT or AST : normal value (vn) 0-29 milliunits (mU) on milliliter (ml)
- GPT or ALT : vn 0-30 mU / ml
- LDH : vn 80-300 mU / ml
- Gt range : vn 5-36 mU / ml in humans; 4-23 mU / ml in women
- FA : vn 20-28 mU / ml
- OCT : vn 8-20 mU / ml
- Aldolase : vn 0.9-6.5 mU / ml
These parameters are the most used and the most sensitive, even if, in reality, these values are not the same standard in all laboratories, since in relation to the different methods performed there may be small differences.
The alteration of the values of transaminases in the blood always indicates the existence of a modification of the normal permeability of the hepatocyte membrane: in case of lesion of the hepatocytes and, a fortiori, in the presence of necrosis, the membrane of these cells will not be able to fulfill the its normal barrier function, thus allowing the release of intracellular enzymes, whose concentration in the blood will therefore be higher than normal levels.
In fact, small quantities of these enzymes are always present in the circulation, even in physiological conditions, so their increase does not represent an "all or nothing" phenomenon, but constitutes a quantitative phenomenon, that is, proportional to the degree of the lesion present at the level of the hepatocyte cell membrane.
Transaminase High - Causes
Transaminase values higher than those considered normal can be determined by various conditions, including:
- hepatitis;
- Obstructive jaundice;
- Cirrhosis and steatosis (fatty liver);
- Liver damage from drugs and chemicals;
- Liver tumors and metastases;
- Cholestatic disorders;
- Heart attack;
- myositis;
- Muscular dystrophies;
- Circulatory decompensation;
- Musculoskeletal trauma;
- Alcoholism;
- Obesity;
- Chronic intestinal diseases;
- Pancreatitis;
- Celiac disease;
- Food allergy;
- Destruction of red blood cells (hemolysis);
- Mononucleosis.
Transaminase levels may also increase following intramuscular injection of drugs or after sustained muscle exercise.
Low transaminase - Causes
Transaminases may have reduced values in the event of:
- Vitamin B6 deficiency;
- Uremia;
- Habitual muscular exercise.
How to measure it
The examination is performed with a normal collection of peripheral blood from the vein of an arm.
Preparation
Transaminase analyzes must be performed fasting for at least 8-10 hours, so that the food does not alter the result. During this period, it is only possible to take a small amount of water. Furthermore, before undergoing blood sampling, you must be in an upright position for at least 30 minutes.
Many drugs interfere with the result, so it is always advisable to inform your doctor if you are following any treatment. It is recommended, then, to abstain from alcohol consumption for at least 24 hours before the test.
Interpretation of Results
Generally speaking, a high transaminase is the signal of a probable affection affecting the liver or biliary tract, but it could also indicate the presence of muscle or cardiac damage.
To get more clues about the causes that produced the abnormal rise of a single transaminase, it is therefore necessary to evaluate, at the same time, the levels of the other liver enzymes. In addition to transaminases, the dosage of bilirubin, prothrombin time and plasma proteins, as well as instrumental diagnostic tests, such as ultrasound or abdominal magnetic resonance imaging, liver biopsy and cholangiopancreatography are also useful for diagnostic framing.
