Alt enzymes is also called as a liver enzymes (or serum enzymes of liver), the liver enzymes play a major role in the normal function of the liver. The most important liver enzyme that is clinically important is
- Serum transaminases or Aminotransferases (they are Aspartate transaminases, and
- Alanine transaminases) SGOT or SGPT.
The estimation of these enzymes is useful in the diagnosis of liver diseases or any other abnormality. The roles of these liver enzymes in the liver are as follows.
AST (Aspartate transaminase) and ALT (Alkaline transaminase) are together known as transaminases. They are in close association with inflammation or injury to liver cells, this condition is known as hepatocellular liver injury. Damage to the liver are also occur due to leak of AST and ALT into the bloodstream.
The aminotransferases constitute a group of enzymes that catalyze the interconversion of aminoacids and 2-oxo-acid by transfer of amino groups. These are two transaminases which are clinically useful.
Alt Enzymes - the Aspartate Transaminase (ast) or Sgot
The Alanine Transaminase (alt) or Sgpt
- It is also called as Serum Glutamate Oxaloacetate transaminase enzyme. It has the normal range of about 4 to 17 IU/L.
- This enzyme was found to be present in higher concentration in Myocardium and livercells.
- The enzyme is also distributed in other tissues via, muscles, pancreas and kidneys.
- Distinct Isoenzymes of Sgot are present in the cytoplasm and Mitochondria of all cells.
- The aminotransfer reaction cataltzed by the aspartate transaminase:
- L-Aspartate + 2-Oxoglutamate $\rightarrow$ Oxaloacetate + L-Glutamate
- The 2-Oxo-Glutamate / L-Glutamate couple serves as one amino group acceptor and donar pair in their amino transfer reaction.
- It is also called as Serum Glutamate pyruvate Transaminase.
- Normal range is 3 to 15 IU/L.
- This enzyme is found rich in mainly in liver cells.
- The amino transfer reaction catalyzed by the Alanine tranaminase (ALT) is:
- L-Alanine + 2-Oxoglutamate $\rightarrow$ Pyruvate + L_Glutamate
- The 2-Oxoglutamate / L-Glutamate couple serves as one amino group acceptor and donor pair in this amino transfer reaction.
The above two reactions catalyzed by the AST and ALT are reversible. The Pyridoxyl 5- phosphate and its amino analogue Pyridoxamine 5-p function as co-enzyme in the amino transfer reaction.
The p-5-p is bound to the apoenzyme and serve as a true prosthetic group. The p-p bound to the apoenzyme accepts the amino group from the first substrate, aspartate or alanine to form enzyme-bound pyridoxamine-5-phosphate and the first reaction product, oxaloacetate pr pyruvate respectively. The coenzyme in amino form then transfers its amino group to the second substrate, 2-Oxoglutarate, to form the second product, Glutamate. P-p is then regenerated.
Serum or crude tissue extracts contain mainly holoamino transferases (enzyme with bound coenzyme). So it is not necessary to add p-5-p to demonstrate some amino transferse activity. However to prosthetic group is progressively lost throughout the purification of tissue extracts, more easily in the case of AST than ALT, so greater activity results when p-5-p is added.
The increased activity can sometimes be seen in the case of reference materials containing partially purified aminotransferases; the presence of p-5-p may produce a marked increase in enzyme activity. Addition of the coenzyme to such materials in now becoming a more common practice. Both holoamino transferases and the coenzyme deficient apoenzyme may be present in the serum. Therefore, addition of p-5-p under conditions that allow recombination with the enzymes can produce a marked increase in aminotransferse activity.
In case of any hepatic disease or any other inflammations to the liver, ALT enzyme is characteristically as high as or higher than AST, and the ALT enzyme ration becomes greater than unity.