Aspartate ammonia-lyase

ASPARTYLCLUCOSAMINIDASE ASPARTATE AMINOTRANSFERASE ASPARTATE AMMONIA-LYASE ASPARTATE CARBAMOYLTRANSFERASE ASPARTATE a-DECARBOXYLASE ASPARTATE /3-DECARBOXYLASE ASPARTATE KINASE d-ASPARTATE OXIDASE ASPARTATE RACEMASE... 

A single enzyme, L-aspartate ammonia lyase obtained from E. coli is used acting on ammonium fumarate substrate. Little cell activity was lost upon immobilisation. Initially polyacrylamide was used as the immobilisation medium, and later cross-linked K-carrageenan was used, as higher operational life-times for the biocatalyst were obtained. The immobilized cell activity is very stable with a half-life of 120 days, while achieving 95% conversion of substrate into product. 

Other enzymes that catalyze elimination reactions that produce fumarate are aspartate ammonia-lyase (aspartase),63 argininosuccinate lyase (Fig. 24-10, reaction g),64/65 and adenylosuccinate lyase... 

Fig. 25-15). In every case it is NH3 or an amine, rather than an OH group, that is eliminated. However, the mechanisms probably resemble that of fumarate hydratase. Sequence analysis indicated that all of these enzymes belong to a single fumarase-aspartase family.64 65 The three-dimensional structure of aspartate ammonia-lyase resembles that of fumarate hydratase, but the catalytic site lacks the essential HI 88 of fumarate hydratase. However, the pKa values deduced from the pH dependence of Vmax are similar to those for fumarase.64 3-Methylaspartate lyase catalyzes the same kind of reaction to produce ammonia plus czs-mesaconate.63 Its sequence is not related to that of fumarase and it may contain a dehydroalanine residue (Chapter 14).66... 

Aspartate aminotransferase 57s, 135s, 753 absorption spectra 749 active site structure 744 atomic structure 750 catalytic intermediates, models 752 NMR spectra 149 quinonoid intermediate 750 Ramachandran plot 61 sequence 57 transamination 742 Aspartate ammonia-lyase 685 Aspartate carbamoyltransferase 348s active sites 348 regulation 540... 

Historically, L-aspartic acid was produced by hydrolysis of asparagine, by isolation from protein hydrolysates, or by the resolution of chemically synthesized d,L-aspartate. With the discovery of aspartase (L-aspartate ammonia lyase, EC 4.3.1.1),57 fermentation routes to L-aspartic acid quickly superseded the initial chemical methods. These processes are far more cost effective than the fermentation routes, and aspartate is now made exclusively by enzymatic methods that use variations of the general approach outlined in Scheme 2.19.53-57-65... 

Lyases are an attractive group of enzymes from a commercial perspective, as demonstrated by then-use in many industrial processes.240 They catalyze the cleavage of C-C, C-N, C-O, and other bonds by means other than hydrolysis, often forming double bonds. For example, two well-studied ammonia lyases, aspartate ammonia lyase (aspartase) (E.C. 4.3.1.1) and phenylalanine ammonia lyase (PAL) (E.C. 4.3.1.5), catalyze the trans-elimination of ammonia from the amino acids, l-aspartate and L-phenylalanine, respectively. Most commonly used in the synthetic mode, the reverse reaction has been used to prepare the L-amino acids at the ton scale (Schemes 19.30 and 19.31).240 242 These reactions are conducted at very high substrate concentrations such that the equilibrium is shifted, resulting in very high conversion to the amino acid products. 

Thus, for aspartase (aspartate ammonia-lyase) the reaction direction is L-aspartate - fumarate + NH 3. The enzyme uses L-aspartate but not the D-enantiomer the product is fumarate not maleate. Hence, this enzyme has strict substrate and product selectivity. For greater detail, this could read strict substrate enantioselectivity and product diastereoselectivity. If necessary, information concerning prochirality could be conveyed in the same way for this same enzyme there is substrate diastereoselectivity for the protons at C-3. 

Aspartate ammonia-lyase was also used to provide (25,3/ )-[3-2H]aspartic acid, and the latter was converted (NH2 - Br -> H) to (2R)-[2-2H]succinic acid [99]. Since the stereochemical assignment for aspartate ammonia-lyase also relies on the configuration of malic acid, this synthesis does not provide an unambiguous verification of the succinate configuration. 

Other enzymes that catalyze elimination reactions that produce fumarate are aspartate ammonia-lyase... 

A biocatalytic enantioselective addition of ammonia to a C=C bond of an a,)9-unsaturated compound, namely fumaric acid, makes the manufacture of L-aspartic acid possible on an industrial scale. This process, which is applied by, e. g., Kyowa Hakko Kogyo and Tanabe Seiyaku, is based on the use of an aspartate ammonia lyase as a biocatalyst [119]. Another comparable reaction is the asymmetric biocatalytic addition of ammonia to trans-cinnamic acid, which represents a technically feasible process for the production of L-phenyl-alanine [120]. 

PAL/TAL both belong to the L-amino acid ammonia lyase family, which catalyzes the formation of various a,/3-unsaturated acids by elimination of ammonia (ammonium ion) from the corresponding L-ct-amino acids. This family of proteins includes aspartate ammonia lyase (AAL), methylaspartate ammonia lyase (MAL), HAL,... 

Aspartate ammonia lyase Bacteria Production of L-aspartic acid... 

On the other hand, the biocatalytic enantioselective addition of hydrazine, hydroxylamine, methoxylamine, and methylamine to fiimarate has been described employing aspartate ammonia lyase [97]. Other enzyme-catalyzed procedures include the addition of ammonia to substituted cinnamic acids employing phenylalanine aminomutase [98, 99]. 

Aspartate ammonia lyase, aspartase (EC 4.3.1.1) an enzyme found in bacteria, higher plants and a few lower animals, which catalyses the reversible interconversion of aspartate and fumarate plus ammonia ... 

The transport of ammonia appears to occur through cell wall ammonia membrane channels called ammonia transporters (Amt proteins). Ammonia, having been transported, is, at least in principle, capable of being utilized by, for example, the enzyme aspartase (aspartate ammonia-lyase, EC 4.3.1.1) that catalyzes the reversible deamination of aspartate (Asp, D) to fumarate (Equation 12.2). 

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