Transaminases are a class of enzymes that catalyze reactions between alpha-keto acids and amino acids. They play a vital role in the use of amino acids in the construction of proteins.
All cells require proteins to perform their functions. Transaminases help in constructing the building blocks that cells need from the raw materials available - mainly proteins.
Animals will often metabolize proteins and derive energy from amino acids when levels of protein are low. During evolution, there were often times when cells had to adapt to consuming non-glucose-derived energy, especially in times of famine, fasting, hibernation, or seasonal variation in the food supply. It makes sense, therefore, that enzymes would exist to facilitate the production of energy from the proteins contained within the cell.
Transaminases perform transamination reactions in which the NH2 amine group from the amino acid is exchanged for the O group on the keto acid. Here, the keto acid becomes an amino acid, and the amino acid becomes a keto acid.
The vast majority of transaminases work on proteins. There is some evidence, however, of transaminase activity on the ribosome, also placing them in the class of RNA enzymes. For instance, researchers have detected activity on the hammerhead and hairpin ribozymes.
Transaminases work according to several steps.
First, these enzymes require the presence of coenzyme pyridoxal-phosphate.
When an amino acid is converted into a keto group acid, the coenzyme is changed into pyridoxamine.
The enzymatic version of pyridoxamine then reacts with alpha-ketoglutarate, oxaloacetate, or pyruvate to give glutamic acid, aspartic acid, and alanine, respectively.
All of these reactions is that they are reversible. You can start with an excess of amino acids and convert them into keto acids and vice versa.
Transaminases, therefore, appears to be an evolutionary response designed to maintain cell homeostasis.
The reversibility of the process has exciting applications in biochemistry. Researchers can use any of the reactants mentioned above to convert between two chemicals with distinct properties.
In animals, trasaminases work in a variety of settings.
In the liver, for instance, transaminases for oxaloacetate or alpha-ketoglutarate are essential for amino acid metabolism. Their presence allows the liver to produce urea and excrete excess nitrogen.
Transaminases play a vital role in muscle too. Evidence suggests that transaminase allows the conversion of pyruvate into alanine, forming an essential part of the glucose-alanine cycle.
As discussed above, many animals need to consume protein in their bodies to produce the energy that they need to survive during periods of fasting. Transaminases, therefore, are also involved in gluconeogenesis - or the formation of new glucose from amino acids. Pyruvate, for instance, is a vital precursor for gluconeogenesis. Without it, cells in the brain and other tissues would not be able to get the energy that they need in periods of extended fasting.
Transaminase detection is also an important diagnostic tool for a variety of diseases. High levels of transaminase, for instance, could be a sign of heart and liver damage, suggesting that the body is unable to clear certain nitrogen-containing compounds from the system.