Methyl amine dehydrogenase

Tryptophan tryptophanylquinone (TTQ). This recently discovered quinone cofactor is similar to the lysyl tyrosylquinone but is formed from two trypto-phanyl side chains.466 It has been found in methyl-amine dehydrogenase from methylotrophic gramnegative bacteria467-469 and also in a bacterial aromatic amine dehydrogenase.470... 

We have been interested in the biological electron transfer between the cofactor tryptophan tryptophylquinone (TTQ) and a type I copper center." " The former is part of the membrane enzyme, methyl amine dehydrogenase (MADH), while the latter is the redox center of the blue copper protein. 

Amicyanin is found in methylotrophic bacteria that can use methylated amines as an energy source. The inactivation of the amicyanin gene in Paracoccus denitrificans results in complete loss of its ability to grow on methylamine, a direct indication that amicyanin is a key component of the methylamine driven electron-transfer chain. Amicyanin accepts an electron from methylamine dehydrogenase and transfers it to a c-type cytochrome (see Section 5.4.5). Currently, more than a dozen amicyanin and pseudoazurin sequences are available. 

PS—polystyrene UF—urea-formaldehyde resin glut—glutaraldehyde thio— thiourea BSA—bovine serum albumin PHEMA—poly(hydroxyethyl methacrylate) IDA—iminodiacetic acid LDH—lactate dehydrogenase OPS—o-phosphoserine 8HQ—8-hydroxyquinoUne Bpa— bis(2-pyridyl-methyl) amine. 

The vast majority of amino acid dehydrogenases use ammonium ions as the amine donor. However, recently a novel N-methyl-L-amino acid dehydrogenase (NMAADH), from Pseudomonas putida, was isolated and used to synthesize N-methyl-L-phenylalanine 36 from phenylpyruvic acid 31 and methylamine 35 in 98% yield and greater than 99%e.e. (Scheme 2.15). The enzyme was shown to accept a number of different ketoacids and also use various amine donors. Glucose dehydrogenase from Bacillus suhtilis was used to recycle the NADPH cofactor [17]. 

In addition to stereoselective metalation, other methods have been applied for the synthesis of enantiomerically pure planar chiral compounds. Many racemic planar chiral amines and acids can be resolved by both classical and chromatographic techniques (see Sect. 4.3.1.1 for references on resolution procedures). Some enzymes have the remarkable ability to differentiate planar chiral compounds. For example, horse liver alcohol dehydrogenase (HLADH) catalyzes the oxidation of achiral ferrocene-1,2-dimethanol by NAD to (S)-2-hydroxymethyl-ferrocenealdehyde with 86% ee (Fig. 4-2la) and the reduction of ferrocene-1,2-dialdehyde by NADH to (I )-2-hydroxymethyl-ferrocenealdehyde with 94% ee (Fig. 4-2lb) [14]. Fermenting baker s yeast also reduces ferrocene-1,2-dialdehyde to (I )-2-hydroxymethyl-ferro-cenealdehyde [17]. HLADH has been used for a kinetic resolution of 2-methyl-ferrocenemethanol, giving 64% ee in the product, (S)-2-methyl-ferrocenealdehyde... 

Figure 5. Methyl viologen-mediated electroreductive amination of a-ketoglutarate using ferre-doxin-NADP-reductase (FNR) as the regeneration enzyme and L-glutamate dehydrogenase (l-GluDH) as the production enzyme [35].

Significant research on LM enzyme encapsulation systems has also been conducted at the University of Hannover, West Germany. Scheper et al. (19) proposed the use of LMs to resolve racemic D,L-phenylalanine methyl ester with encapsulated chymotrypsin. This enzyme cleaves the ester bond of the L-isomer only. The process employed Adogen 464 (TOMAC) as an anion carrier, but the pHs used were such that any L-phenylalanine formed would be zwitterionic LM transport of zwitterions would be expected to be poor. Further work has included development of an LM enzyme reactor for detoxification of blood (33), reductive amination of a-ketoisocaproate by L-leucine dehydrogenase with a coencapsulated... 

FIGURE 57-3. Dopamine metabolism in presynaptic dopamine neuron (see text for full details). 30MD, 3-O-methyldopa AC, adenylate cyclase AD, aldehyde dehydrogenase COMT, catechol-O-methyl transferase D1-D3, dopamine receptors DA, dopamine DAT, dopamine transporter DOPAC, 3,4-dihydroxyphenylacetic acid HVA, homovanillic acid r-AAD, r-aromatic amine decarboxylase MAO-B, monoamine oxidase B TH, tyrosine hydroxylase. 

Starting from 2-oxo acids, various optically pure (S)-amino acids can be quantitatively synthesized by using PheDII and formate dehydrogenase. Tabic 8 shows the yields of the (S)-amino acids thus synthesized. The reductive amination products derived from (3/ /,S )-3-methy 1-2-ox ovaierate and (37 /5)-3-methyl-2-oxo-3-phenylpyruvate have been identified as diastereomeric mixtures of (S)-isoleucine and (S)-alloisoleucine, and (2S,3f / S)-2-amino-3-methyl-3-phenyl-propionic acid, respectively. The product from 2-oxo-5-phcnylvalerate solidified as the reaction proceeded. 

High-resolution H n.m.r. spectroscopy has been used to probe the conformations of a number of o-ribofuranosylamine derivatives and such rigid molecules as 2,2 -cyclonucleosides and nucleoside 3, 5 -phosphates in aqueous solution. H N.m.r. spectroscopy has also been used to study details of the intramolecular association and conformations of a- and j8-linked pyridine ribo-nucleosides and their 5 -phosphates. The results were analysed in terms of base-D-ribose, o-ribose-side-chain, and base-side-chain interactions and the conformational restraints imposed by the cis HO-2-HO-3 interaction in jS-nucleo-tides and the additional cis HO-2 -base interaction in a-nucleotides. H N.m.r. measurements - including measurements of nuclear Overhauser effects and paramagnetic relaxations effected by Mn + cations - have been used to investigate the preferred conformation about the jV-glycosidic bond of 8-amino-, 8-methyl-amino-, and 8-dimethylamino-adenylic acid, all of which competitively inhibit the coenzyme NADH in the reaction with chicken-muscle lactate dehydrogenase. The primary and secondary amines were shown to prefer anti conformations, whereas the tertiary amine prefers a syn conformation. 

Deracemizatlon of racemic mexiletine (di-o-methyl-phenoxyisopropylamine) is successfully achieved in a simple two-step procedure. This work extends the utility of the TA to include deracemizatlon of amines and the asymmetric synthesis of ketones to bypass the limitations of kinetic resolution. The cofactor is recycled by amino acid oxidase [73] in the first deracemizatlon step and by dehydrogenases in the second asymmetric synthesis step [47a,74]. In addition, both enantiomers of mexiletine can be obtained by simply switching the order of the addition of stereospecific TAs. 

Figure 7.26 Methyl phenidate is used to treat ADHD. Its structure includes a cyclic amine. The process of metabolic dealkylation can occur on the unsubstituted position adjacent to the nitrogen giving rise to a carbinolamine, which can be hydrolyzed to an aldehyde and an amine. However, since the substrate was a cyclic amine these two new functional groups remain part of the same molecule. The aldehyde can be further oxidized to a carboxylic acid and this can react with the amine by elimination of water to form a lactam. Alternatively, the carbinolamine can be oxidized by alcohol dehydrogenase to directly give the same lactam, which is observed as a major metabolite of methyl phenidate.

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