L-amino acid deaminase

An amino acid is deaminated when it loses its nitrogen in the form of NH3 and generates an a-keto acid. It is a redox reaction using NAD+, FAD, or FMN as cofactors, and it may occur in either the mitochondria or the cytosol. The most potent l amino acid deaminase is glutamate dehydrogenase, which catalyzes the reaction... 

The procedure reported in Scheme 13.11 describes deracemization of an amino acid involving oxidation with an L-specific enzyme and transamination with a D-amino transferase using D-aspartate 10, which is generated from L-aspartate 11 by aspartate racemase, as the amino donor. The oxidative enzyme is defined as an L-amino acid deaminase, a flavoprotein from Proteus myxofadens [34]. The transamination reaction is shifted towards the product since the oxalacetate 12 formed decarboxylates spontaneously to give pyruvate and carbon dioxide. 

Recently, L-amino acid deaminase (EC 1.4.3.x) activities have been identified, particularly from the Proteus genus [59]. This enzyme, constituted by 370 residues, is an FAD-containing L-amino acid oxidase flavoprotein that uses molecular oxygen to convert L-amino acids into the corresponding a-keto adds and ammonia but does not produce hydrogen peroxide. L-amino acid deaminase prefers amino acids with aliphatic, aromatic, and sulfur-containing side chains (the best substrates are L-heu, L-Phe, L-Met, and L-Trp) and its kinetic efficiency is quite low because of the low Vnm value (<2 units/mg protein). 

A range of (D)-amino acids is also accessible by a fermentation route. The microorganisms are for this purpose modified, so that they no longer express functional (D)-amino acid deaminases. However, they contain instead genes for (L)-amino acid deaminases, (D)-amino acid aminotransferases and a special racemase. Monsanto, for example, has patented such an approach for the preparation of (D)-phenylalanine. 

A racemase brings about inversion of the relatively cheap (L)-isomers of alanine or aspartic acid, but not of (D)-phenylalanine. Only (L)-phenylalanine is deaminated by an (L)-amino acid deaminase, whereas (D)-phenylalanme is not. The latter is generated by ammonia transfer from (D)-alanine or (D)-aspar-tic acid with a (D)-amino acid aminotransferase. The equilibria are moved in favour of the product, either by the metabolism of pyruvic acid or oxosuccinic acid. Since (L)-amino acid deaminases, like (D)-amino add aminotransferases, are non-specific, they also permit the preparation of a variety of other (D)-amino acids. [58]... 

Liu L, Hossain GS, Shin HD, Li J, Du G, Chen J. One-step production of a-ketoglutaric acid from glutamic acid with an engineered L-amino acid deaminase from Proteus mirahilis. J Biotechnol 2013 164 97-104. 

Even though this concept has been proven to be effective, the toxicity of NaCNBHj led to the search for alternative reagents whereby amine-boranes turned out to be competent substitutes [117]. They are stable in water at neutral or basic pH and soluble and unreactive toward a wide range of protic and aprotic solvents. Deracemization of several natural and nonnatural AAs with an L-amino acid deaminase (l-AAD)... 

Multienzyme cascade for the conversion of i-amino acids to a-hydroxy acids employing an L-amino acid deaminase (l-AAD) and isocaproate reductases (Hie). 

Because the commercial availability of 2-oxo acids is somewhat limited and their chemical stability is relatively poor, a system was developed to generate these in situ using an amino acid deaminase (amino acid oxidase, E.C. 1.4.3.x) (Scheme 19.3) A This keto acid was then reduced to the chiral 2-hydroxy acid with either L-LdH or D-LdH to produce the respective enantiomer in moderate to high yield with high enantiomeric purity.49... 

Enzyme electrodes for lactate determination using immobilized lactate dehydrogenase 16), for urea determination using immobilized urease 17), for L-amino acids using immobilized L-amino acid oxidase 18), and for various amines using the appropriate immobilized deaminase system (19) have also been prepared. A urease electrode is commercially available from Beckman,... 

The a-keto acid substrates are available by chemical synthesis. They are also accessible by enzymatic methods, such as amino acid deaminase, that generate these substrates from inexpensive L-amino acids. 

A variety of other enzymes involved in amino acid catabolism have been detected in both protozoa and helminths. These include deaminases such as histidase, decarboxylases, some of which are involved in biosynthesis of amines and related compounds, and hydroxylases of proline, tryptophan and tyrosine. These additional enzymes have mostly been reported in helminths (1). L-Amino acid oxidases and D-amino acid oxidases are also present and the availability of the latter would allow D-amino acids to be metabolized in the absence of amino acid racemases. 

Compared to chemical synthesis, enzymatic transformation has several potential advantages, including its ecofriendly nature, low energy consumption, and reduced production cost. However, to date, there have been few reports on the enzymatic synthesis of a-KG. However, a-KG has been produced from L-glutamic acid by using amino acid deaminase. ... 

D-glucose as the chiral starting material, the former being converted to a 4-amino-4-deoxy-D-mannose intermediate, the latter to a 3-amino-3-deoxy-D-mannose derivative. The adenosine deaminase inhibitor (+)-EHNA (60) has been prepared using L-ascorbic acid as the source of the chiral oxiran precursor (61). 

One of these compounds, 9-(p-bromoacetamidobenzyl) adenine, has been used for labeling the amino acid residues of the active site. In fact the functional groups of adenosine deaminase are particularly unreac-tive. The sulfhydryl groups present in the catalytic site react with p-mercuribenzoate and phenylmercuriacetate, but not with haloacetates, haloacetamides, iV-ethylmaleimide, or 5,5 -dithiobis-(2-nitrobenzoic acid). The enzyme is inactivated by l-fluoro-2,4-dinitrobenzene and by haloacetates at pH values over 7.5 and 9.0, respectively more than one lysine residue is modified under these conditions. ... 

On the other hand, a-transaminases have been used extensively in the production of amino acids through kinetic resolution and asymmetric synthesis. While many studies rely on the use of an excess of cosubstrate to drive the reaction to completion, some multienzymatic approaches have been developed as well. As an example, aspartate has been used as an amino donor in a multienzymatic synthesis of L-2-aminobutyrate from L-threonine (Scheme 4.8). ° The rather complex multistep sequence started with the in situ formation of 2-ketobutyrate from L-threonine catalysed by threonine deaminase (ThrDA) from E. coli. A tyrosine transaminase (lyrAT) from E. coli converted 2-ketobutyrate and L-aspartie acid to L-2-aminobutyrate and oxaloacetate, which spontaneously decarboiq lated to give pyruvate. Since the... 

The enzyme occurs in mammalian liver and kidney, from which sources Krebs (1935) has separated two types L-deaminase, which attaclcs the natural amino acids, and which can be inhibited by octyl alcohol and D-deaminase, which oxidised the optically isomeric D-amino acids, and is not inhibited by octyl alcohol. Since these D-acids are foreign to living organism and not found in food proteins, the significance of their deaminase is obscure, unless it be to protect the animal from evolutionary freaks of metabolism and malignant growths (p. 136). 

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