483 Lecture 4 - Glutamate Oxaloacetic Acid Transaminase (GOT) Purification -- Expt 3 Part A
1. Glutamate Oxaloacetate Transaminase (GOT)
Glutamate Oxaloacetate Transaminase (GOT) catalyzes the transfer of an amino group from an amino acid (Glu) to an 2-keto-acid to generate a new amino acid and the residual 2-keto-acid of the donor amino acid:
Since the reaction catalyzed by GOT is completely reversible, I illustrate it here with Asp (an amino acid) as the donor of the amino group which will be transferred to the acceptor 2-keto group of the 2-keto-glutarate, which we sometimes call alpha-keto-glutarate. I wrote it this way since the official name of GOT is actually Aspartate Transaminase (EC 2.6.1.1). It is worth noting that the name "transaminase" can be replaced by "aminotransferase", which is useful to know since the class 2 enzymes are all called transferases. The Enzyme Commission number (EC 2.6.1.1) is a use way to link to a Web page with properties of all enzymes which are known. At the web page for EC 2.6.1.1 you can find a list of properties of GOT and links to other databases with information on GOT including amino acid sequences and other data.
Transaminase, including GOT, are dependent on the cofactor pyridoxal phosphate, which has vitamin b-6 as it's core:
This cofactor provides an aldehyde group to the enzyme, which is not available among the side chains of the 20 amino acids found in proteins. The phosphate group is added to the vitamin b-6 in our food and food supplements after it is ingested. The phosphate group provides a way to bind the cofactor to the enzyme via a strong ionic interaction. The aldehyde group readily reacts with primary amines like the alpha-amino groups of amino acids. This process activates the amino group so that it can be cleaved by water. This releases the keto-acid core of the amino acid and leaves the amino group on the enzyme. Now the acceptor keto-acid binds and reacts with the activated amino group to form the new amino acid. To illustrate how the resting enzyme looks, an amino group of an active site Lys's side chain amino group is shown bound to the cofactor in the GOT active site:
This resting form of GOT is ready for accepting the amino group of a donor amino acid (Glu or Asp), after the Schiff's base has been cleaved with water. The active site of the GOT also has amino acid side chains controlling the amino acids which bind and will act as donors of the alpha-amino group. In other words, the active site controls the substrate specificity of transaminases.
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