TRANSAMINASES
Transamination
is the process in which an amino group is transferred from amino acid to an α-keto
acid, while the enzymes responsible for transamination are called Transaminases
(Nelson et al, 2000). Transaminases
are classic examples of enzymes catalyzing bimolecular ping-pong reactions in
which the first substrate reacts then the product must leave the active site
before the second substrate can bind. Thus the incoming amino acid binds to the
active site, donates its amino group to pyridoxal phosphate and departs in the
form of an α -keto acid. The incoming α -keto acid then binds accepts the amino
group from pyridoxamine phosphate and departs in the form of an amino acid
(Nelson et al, 2000).
Figure: Enzyme-catalyzed
Transamination; all
Transaminases have pyridoxal phosphate (PLP) as cofactor.
The two transaminases of diagnostic
importance are:
(1)
Serum
glutamic oxaloacetate Transaminase (SGOT) or Aspartate amino transferase (AST),
and
(2)
Serum
glutamic pyruvate Transaminase (SGPT) or Alanine amino transferase (ALT). While
AST is found in every tissue of the body, including red blood cells and is
particularly high in the cardiac muscles, ALT is present in moderately high
concentration in liver and low in cardiac, skeletal muscle and other tissues.
Both AST and ALT measurements are useful in the diagnosis and monitoring of
patients with hepatocellular disease.