Transamination, taken literally, means the transfer of an amino group from one molecule to another. In many organisms, this process is used both to synthesize and to degrade amino acids. One of the primary cellular benefits of the reaction is that it allows the transfer of an amino group without the formation of ammonia, which is a toxic byproduct. In humans, it occurs primarily in the liver, and is also known as aminotransfer.
Biochemically, this is an oxidation-reduction reaction that transfers the amino group from an amino acid to an alpha-keto acid. This results in the creation of a new amino acid and a new alpha-keto acid. By this definition, interconversion may actually be a better term to describe the exchange of amino groups. The alpha-keto acids formed can be converted into lipids, glucose, or glycogen. In this way, proteins obtained by dietary consumption can be used for current or future cell energy needs.
Transamination is also critical in humans for anabolic functions, such as the synthesis of non-essential amino acids. Humans need approximately 20 amino acids to build proteins, which are required to synthesize hormones and enzymes, and are involved in many physiologic functions. Eight amino acids are called essential, and must be obtained from dietary intake. The remaining amino acids are termed non-essential because the body can use other substances to synthesize them.
Of the non-essential amino acids, alanine, aspartate, and glutamate are among the most common. Glutamate is synthesized from alpha-ketoglutarate. This alpha-keto acid is created during the metabolism of dietary protein. Glutamate can then undergo transamination to form alanine and aspartate. All other non-essential amino acids are formed from these three.
Aminotransfer is facilitated by enzymes called aminotransferases or transaminases. These enzymes have broad activity, meaning that they can catalyze reactions with several different amino acid types. For activity, a co-factor is required and acts as an intermediate carrier of the amino group during the reaction. For transaminases, the required co-factor is pyridoxal phosphate, which is the active form of vitamin B6.
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are the two most common human transaminases. These two enzymes are found in many tissues in the body, including the liver and heart. If those tissues are damaged due to disease, the damaged cells release the enzymes into the bloodstream. Healthcare practitioners often measure ALT and AST in the blood to diagnosis and monitor damage to the liver.