Aspartate asparagine synthesis

The non-essential amino acids are alanine, arginine, aspartate, asparagine, cysteine, glutamate, glutamine, glycine, proline, serine and tyrosine. A summary of the reactions involved in their synthesis is given in Figure 8.3 and full details of these pathways are provided in Appendix 8.2. 

The aspartate (oxaloacetate) family of amino acids includes aspartate, asparagine, methionine, lysine, threonine, and isoleucine (see fig. 21.1). The pyruvate family includes alanine, valine, leucine, and also lysine and isoleucine (see fig. 21.1). Threonine is a precursor of isoleucine. It is converted into isoleucine by a group of enzymes that are also used in the synthesis of valine (fig. 21.10). 

The formation of asparagine from aspartate is chemically analogous to the formation of glutamine from glutamate. Both transformations are amidation reactions and both are driven by the hydrolysis of ATP. The actual reactions are different, however. In bacteria, the reaction for the asparagine synthesis is... 

It has been suggested that this pathway not only seems to supply the carbon skeletons for asparagine synthesis, but is also useful for reassimilating the large quantities of COg liberated in an actively fixing nodule (Christel-ler et al., 1977 Atkins et ai, 1978). Presumably C4 plants, which contain large amounts of the enzyme in the leaf mesophyll cells, are able to form aspartate for asparagine synthesis in a similar manner (for a comprehensive review see Hatch, 1978). 

Arrhenius, Svante, 86,353 Arsenic, 573-574 Asparagine, 622t Aspartic acid, 622t Aspirin. See Acetylsalicylic acid Astaxanthin, 157 Asymmetric synthesis, 601 Atherosclerosis, 604... 

L-Asparaginase is an enzyme that may be produced by Escherichia coli. Asparaginase hydrolyzes the reaction of asparagines to aspartic acid and ammonia to deplete lymphoid cells of asparagine, which inhibits protein synthesis. The... 

Soroka, M. and Mastalerz, P., The synthesis of phosphonic and phosphinic analogs of aspartic acid and asparagine, Rocz. Chem., 50, 661, 1976. 

Asparaginase Asparaginase is an enzyme that hydrolyzes L-asparagine to L-aspartic acid, which causes a depletion of reserves of L-asparagine, thus inhibiting protein and nucleic acid synthesis. It is effective for severe lymphocyte leukemia [154]. A synonym of this drug is elspar. 

A third mechanism of synthesis, which was only recently recognized, appears to provide the sole source of asparagine for many bacteria.98b The asparagine-specific transfer RNA tRNAAsn is "mischarged" with aspartic acid to form Asp-tRNAAsn. This compound is then converted to the properly aminoacylated Asn-tRNAAsn by a glutamine-dependent amidotransferase. (The entire ATP-dependent sequence is shown in Eq. 29-6.) The activated asparaginyl group is then transferred from Asn-tRNAAsn into proteins as they are synthesized. 

Four mechanisms have been advanced for the prebiotic formation of amino acids. The first involves a cyanohydrin (reaction 2) and a related route (reaction 3) can be invoked to account for the presence of hydroxy acids. These particular reactions have been studied in considerable detail both kinetically and in terms of thermodynamic quantities.347 An alternative route (4) involves the hydrolysis of a-aminonitriles, which are themselves formed directly in anhydrous CH4/NH3 mixtures.344 Cyanoacetylene, formed in CH4/N2 irradiations,349 yields significant amounts of asparagine and aspartic acids (reaction 5). Finally, a number of workers336,350"354 have proposed that HCN oligomers, especially the trimer aminoacetonitrile and the tetramer diaminomaleonitrile, could have been important precursors for amino acid synthesis. Reaction mixtures involving such species have yielded up to 12 amino acids. Table 11 indicates the range of amino acids produced in these kinds of sparking syntheses. Of some interest is the fact that close parallels between these kinds of experiments and amino acid contents of carbonaceous chondrite meteorites exist.331,355,356... 

Fig. 1.3 Reactions showing synthesis of glutamate in brain. Aspartate aminotransferase (1) glu-taminase (2) glutamate dehydrogenase (3) GABA aminotransferase (4) alanine aminotransferase (5) ornithine aminotransferase (6) Al-pyrroline 5-carboxylic acid dehydrogenase (7) and asparagine synthetase (8)...

Fig. 13. Synthesis of (3-linked asparagines glycosides (a) dicyclohexylcarbodiimide (DCC) and l-hydroxybenzotriazole(HOBt) coupling (98), (b) pentafluorophenyl (OPfp) ester of aspartic acid derivative coupling (97).

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