Glutamic acid, 494 Table

Some ammo acids have side chains that bear acidic or basic groups As Table 27 3 indicates these ammo acids are characterized by three values The third pK reflects the nature of the side chain Acidic ammo acids (aspartic and glutamic acid) have acidic side chains basic ammo acids (lysine arginine and histidine) have basic side chains The isoelectric points of the ammo acids m Table 27 3 are midway between the pK values of the zwitterion and its conjugate acid Take two examples aspartic acid and lysine Aspartic acid has an acidic side chain and a pi of 2 77 Lysine has a basic side chain and a pi of 9 74... 

The 20 ammo acids listed m Table 27 1 are biosynthesized by a number of different path ways and we will touch on only a few of them m an introductory way We will exam me the biosynthesis of glutamic acid first because it illustrates a biochemical process analogous to a reaction we discussed earlier m the context of amine synthesis reductive ammatwn (Section 22 10)... 

An estimation of the amount of amino acid production and the production methods are shown ia Table 11. About 340,000 t/yr of L-glutamic acid, principally as its monosodium salt, are manufactured ia the world, about 85% ia the Asian area. The demand for DL-methionine and L-lysiae as feed supplements varies considerably depending on such factors as the soybean harvest ia the United States and the anchovy catch ia Pern. Because of the actions of D-amiao acid oxidase and i.-amino acid transamiaase ia the animal body (156), the D-form of methionine is as equally nutritive as the L-form, so that DL-methionine which is iaexpensively produced by chemical synthesis is primarily used as a feed supplement. In the United States the methionine hydroxy analogue is partially used ia place of methionine. The consumption of L-lysiae has iacreased ia recent years. The world consumption tripled from 35,000 t ia 1982 to 100,000 t ia 1987 (214). Current world consumption of L-tryptophan and i.-threonine are several tens to hundreds of tons. The demand for L-phenylalanine as the raw material for the synthesis of aspartame has been increasing markedly. 

In Foods. Each amino acid has its characteristic taste of sweetness, sourness, saltiness, bitterness, or "umami" as shown in Table 13. Umami taste, which is typically represented by L-glutamic acid salt (and some 5 -nucleotide salts), makes food more palatable and is recognized as a basic taste, independent of the four other classical basic tastes of sweet, sour, salty, and bitter (221). 

The importance of Heinrich Ritthausen s fundamental studies, 1862 to 1899, on analytical procedures for the determination of amino acids in proteins has been emphasized in the biographical sketches which have been presented by Osborne (210), Vickery (289), and Chibnall (47). It is of particular interest to note here the prediction made by Ritt-hausen about 1870 that the amino acid composition would prove to be the most adequate basis for the characterization of proteins. Ritthausen and Kreusler (230) were the first, in 1871, to determine amino acids derived from proteins, and some of the values which they found for aspartic and glutamic acids are given in Table III (cited by Chibnall, 47, and Vickery, 286). 

The digestion of the protein, after heme removal, using Glu-C endoproteinase was also carried out. This enzyme cleaves the polypeptide backbone on the carboxyl terminus of a glutamic acid residue and in this case yielded twelve chromatographic responses. Despite two of these arising from unresolved components, molecular weight information was obtained from 15 polypeptides, one of which was the intact protein, covering the complete sequence, as shown in Table 5.10. 

The amounts of single amino acids excreted in urine in the conjugated form, as determined independently by Stein and Muting, are given in Tables 1 and 2. According to Stein, glycine, glutamic acid, aspartic acid, histidine, and proline are quantitatively the most important amino acids liberated in the course of urine hydrolysis. Serine, lysine, tyrosine, cysteine and cystine, threonine, alanine, valine, phenylalanine, and leucine are... 

There is only a small selection of nonprotein amino acids that contain carbonyl groups in the form of ketone, aldehyde, and carboxylic acid moieties, as part of the side chain. The examples given in Table 6 are components of nonribosomal peptides isolated from bacteria or fungi and siderophores from bacteria. The biosynthesis of these amino acids is not clear however, some of the amino acids with carboxylic acid side chains may be traced back to the L-a-amino acids aspartic acid and glutamic acid. 

Table 1. IFABP-PX60-mediated transamination of a-ketoglutarate to glutamic acid in the presence of various hydrophobic amino acids...

The major metal-binding amino acid side chains in proteins (Gurd and Wilcox, 1956 see Voet and Voet, 1990) (Table II) are carboxyl (aspartic acid and glutamic acid), imidazole (histidine), indole (tryptophan), thiol (cysteine), thioether (methionine), hydroxyl (serine, threonine, and tyrosine), and possibly amide groups (asparagine and glutamine, although... 

Finally, when oxazolones 269 bearing a carboxyalkyl chain at C-4 were used, the separation was effected on the mixture of diastereomeric succinimides 270 and 271. In this case, the resolved amino acid contains both an aspartic acid and a glutamic acid side chain (Scheme 7.87). Selected examples of amino acids that illustrate the general applicability of Obrecht s methodology are shown in Table 7.22 (Fig. 7.24). 

Enolate dianions from 3-benzoyl-2-fc-rt-butylT-methyl-5-oxo-4-imidazolidineacetic and -propanoic acids 4, obtained from aspartic and glutamic acid, have also been used in diastcreose-lective alkylation reactions (see Table 4)7. 

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