2-Oxoglutaric acid transaminations with

Transamination. Transamination with pyridoxal or analogs requires a metal catalyst such as Cu(II). However, transamination can be effected with DPL in combination with hexadecyltrimethylammonium chloride. By using these two reagents phenylglycine undergoes transamination with 2-oxoglutaric acid (equation I). 

Deamination of amino acids in animal tissue is generally effected by transamination with an a-keto-acid. In the majority of cases, this is 2-oxoglutarate formed by the citric acid cycle. Aspartate aminotransferase and alanine aminotransferase are examples of this kind of reaction. In Figure 2.7, transamination involving these enzymes is depicted as it is known to occur in mammalian liver. Note that the scheme shown here requires participation of oxalacetate and pyruvate and thus is intimately connected with metabolic pathways considered earlier. Serine and glycine are readily interconvertible in animal tissue by the enzyme serine hydroxymethyltransferase. It is worth noting also that decarboxylation of serine to ethanolamine as mentioned above can be followed by A -methylation to yield choline. Choline is both an essential component of many... 

Finally, transamination with the branched-chain amino acid transaminase (EC 2.6.1.42), the coenzyme for which is pyridoxal and the source of the amino group from which pyridoxal transfers the nitrogen is glutamate (Glu, E), occurs. 2-Oxoglutarate forms in the process. 

Glutamate is a commonly occurring amino acid that acts as an excitatory transmitter in CNS. The molecule may be synthesized within the nerve ending either by transamination from 2-oxoglutarate (described in Section 6.3.1.1) or by deamination of glutamine (see Section 8.2.2). However, in common with other synaptic signals, there exists an efficient uptake mechanism in the axon to recycle glutamate that has been released. 

The phosphate ester of the aldehyde form of vitamin B6, pyridoxal phosphate (pyridoxal-P or PLP), is required by many enzymes catalyzing reactions of amino acids and amines. The reactions are numerous, and pyridoxal phosphate is surely one of nature s most versatile catalysts. The story begins with biochemical transamination, a process of central importance in nitrogen metabolism. In 1937, Alexander Braunstein and Maria Kritzmann, in Moscow, described the transamination reaction by which amino groups can be transferred from one carbon skeleton to another.139 140 For example, the amino group of glutamate can be transferred to the carbon skeleton of oxaloacetate to form aspartate and 2-oxoglutarate (Eq. 14-24). 

This enzyme is a pyridoxal phosphate protein which catalyses transamination reactions with the aid of 2-oxo-acids other than 2-oxoglutarate. 

Aspartate 4-semialdehyde, seen, for example, in Scheme 12.13, which provided a pathway for the biosynthesis of the essential amino acid methionine (Met, M) and in Scheme 12.14, which holds a representation of the biosynthesis of threonine (Thr, T), is also a place to begin to describe a pathway to lysine (Lys, K). As shown in Scheme 12.19, aspartate 4-semialdehyde undergoes an aldol-type reaction with pyruvate (CHsCOCO ") in the presence of dihydropicoUnate synthase (EC 4.2.1.52) to produce a series of intermediates that, it is presumed, lead to (5)-23-dihydropyridine-2,6-dicarboxylate. Then, dihydrodipicolinate reductase (EC 1.3.1.26) working with NADPH produces the tetrahydropyridine, (S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate.This heterocycle, in the presence of glutamate (Glu, E) and water, is capable of transamination directly to 2-oxoglutarate and (2S, 6S)-2,3-diaminopimelate in the presence of LL-diaminopimelate aminotransferase (EC 2.6.1.83), while the latter, in the presence of the pyridoxal dependent racemase... 

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