3-Methylaspartate 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... 

METHYLASPARTATE AMMONIA-LYASE N-METHYLGLUTAMATE SYNTHASE UREASE... 

METHYLASPARTATE AMMONIA-LYASE B-METHYLASPARTATE-GLUTAMATE MUTASE... 

In the present case an experimental approach to the elucidation of the steric course was facilitated by the observation that a cell-free extract from C. tetanomorphum contained not only the AdoCbl-dependent glutamate mutase, but also a specific ammonia lyase that catalysed the reversible interconversion of mesaconate (2) and (25,35 )-3-methylaspartate (3) (Fig. 4). In the presence of this... 

Arginine or citrulline in concentration in excess of the optimal can inhibit both argininosuccinate synthetase or argininosuccinate lyase in tissue cultures (S6). Whether this is applicable to the conditions of synthesis of the urea in liver is uncertain. a-Methylaspartic acid also specifically inhibits argininosuccinate synthetase (B7, C4, SIO). 

The enzyme methylaspartate ammonia lyase (P-methylaspartase, E.C. 4.3.1.2) is involved in the metabolism of branched pentanoic acids. The enzyme catalyzes the addition of ammonia to mesaconic acid (8) to yield i-tfireo-3-methylaspartate (9) as depicted in Scheme 12.6-3. The enzyme has been shown to be induced under anaerobic conditions in facultative anaerobes such as Citrobacter, Proteus, Escherichia coli and Enterobacter17, 81 and has been applied for the synthesis of 3-substituted (S)-aspartic acid derivatives, such as (2S,3S)-3-methylaspartic acid (9), (2S,3S)-3-ethylas-partic acid (11), and (2R,3S)-3-chloroaspartic acid (13) 7l In addition, a process for the preparation of dialkyl-(2S,3S)-3-ethylaspartates using methylaspartate ammonia lyase has been developed by Merck191. 

Bear et al. have been using methylaspartate ammonia-lyase from Clostridium tetanomorphum to produce optically active pure precursors [3-methyl-, 3-ethyl and... 

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,... 

So, the reversible formation of alkenes currently appears limited to a handful of ammonia lyases that include the already noted aspartate ammonia-lyase that produces fumarate (Equation 12.2), methylaspartate ammonia-lyase that yields mesaconate (EC 4.3.1.2) (Equation 12.3), the urocanate-producing histidine... 

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