Purines aminotransferase

Aspartate can be transaminated to form oxaloacetate, an intermediate of the citric-acid cycle. As with most transaminations, this is a reversible reaction, and aspartate can also be synthesized by a transamination reaction with glutamate and oxaloacetate to form aspartate and a-ketoglutarate. Therefore, aspartate is a nonessential amino acid. The aminotransferase with aspartate and a-ketoglutarate is particularly active in most tissues and occurs both in the mitochondria and the cytosol. The importance of this reaction is greater than simply forming the oxaloacetate or aspartate. Aspartate aminotransferase is an important reaction in the malate shuttle (see Chapter 11) wherein, reducing power can be transferred from the cytosol to the mitochondrion. Aspartate also plays a role in purine and pyrimidine synthesis and is particularly important in pyrimidine synthesis, where it donates both carbon and... 

Biosynthesis metabolism Asp is formed from oxaloacetic acid by aspartate aminotransferase (EC 2.6.1.1) and serves as starting material in the biosyntheses of threonine, methionine, and lysine. The first step is catalysed by aspartate kinase (EC 2.7.24) which only occurs in plants and microorganisms. This enzyme exists as 3 isozymes in Escherichia coli and exhibits a typical example of feedback regulation. Asp plays a central role in the biosyntheses of pyrimidines and purines. In the urea cycle Asp condenses with " citrulline to aigininosuccinate, a stimulating neuro-transmitter. ... 

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