Malic acid malate from fumarate

To diagnose the situation, the malates formed were treated with fumarase. The one formed from (R)-acetyl-CoA became equilibrated with tritiated fumaric acid and retained most of its tritium whereas that from the (S)-acetyl-CoA lost most of its tritium in the reversible dehydration yielding unlabeled fumaric acid (and, then, unlabeled malic acid). Reference to Fig. 58 shows that the former malate was thus 3S and the latter 3R, i.e. the condensation proceeds with inversion of configuration. 

FIG. 21 Schematic diagram for the production of L-malic acid from fumaric acid using a six-compartment (Zi-Z6) ED stack composed of anionic (a) and cationic (c) membranes, as extracted from Sridhar (1987). As ammonium fumarate is formed, it is enzymatically converted into ammonium malate in an external bioreactor (R). The combined system is also provided with a series of storage tanks for the acidic cathode-(Dl) and anode-(D6) rinsing solutions, raw materials (D2), ammonium fumarate (D3), ammonium malate (D4), and final product (D5). 

Wood and coworkers have demonstrated that pigeon liver mince poisoned with malonate is unable to convert C 02 into isotopic succinate but can direct the isotope into malate and fumarate as well as into the a-carboxyl of a-ketoglutarate (see Fig. 5). On the other hand, non-poisoned liver possesses the ability to anaerobically fix C 02 in succinic acid as well as fumaric and malic acids. The dicarboxylic acids invariably contain the isotopic carbon predominantly in their respective carboxyl groups. These important experiments provide conclusive proof for two main concepts. First, that malonate specifically inhibits succinic acid dehydrogenase and hence blocks completely the formation of succinic from fumaric acid. Secondly, there must be two routes by which succinate is formed. By the first pathway, pyruvate can condense with... 

Battat et al. [87] used A. flavus ATCC 13697 as the biocatalyst for the production of malic acid from glucose in a 16-1 stirred-tank fermentor. The optimal fermentation conditions are as follows agitation rate, 350 rpm Fe +, 12 mg/1 nitrogen (as ammonium sulfate), 271 mg/1 phosphate, 1.5 mM. Total amount of CaCOj added was 90 g/1. Fermentation was carried out at 32 °C for up to 200 h. Under the aforementioned conditions, 113 g/1 of L-malic acid were produced from 120 g/1 glucose utilized with an overall productivity of 0.59 g/l/h. Based on the molar yield, it was 128% for mahc acid and 155% for total acid (malic, fumaric and succinic acid). The increase in acid accumulation during the course of incubation coincides with the increase in the activities of NAD -malate dehydrogenase, fumarase and citrate synthase. 

The stereospecific formation of the S enantiomer of malic acid from fumaric acid also occurs in the tricarboxylic acid (TCA) cycle. The (5)-(-)-malic acid that is produced is converted to oxaloacetic acid by the enzyme malate dehydrogenase. 

In general, endogenous metabolism of anaerobic bacteria was found to be more stable, when biocatalysts based on immobilized cells of P. shermanii and E. coli were compared with respect to the reactions shown above (Ikonnikov, 1985). P. shermanii had a higher aspartase activity than P. pentosaceum, P. petersonii and P. technicum (Kalda and Vorobjeva, 1981). After 3 days of incubation with continuous stirring at 37°C and pH 8.5, the extent of substrate conversion (ammonium fumarate) was 95-96% and 75-90% in the case of E. coli K-12 and P. shermanii, respectively. In addition to aspartic acid, the reaction mixtures of the two strains also contained malic acid. Heat treatment of the biomass of P. shermanii (50 C, 1.5 h, pH 5.0) resulted in a complete inactivation of fumarase, while the activity of aspartase was retained (Kalda and Vorobjeva, 1980, 1981). As a result of the elimination of fumarase activity, the yield of L-aspartic acid from ammonium fumarate was increased up to 96-98% the incubation time was also shortened since no substrate was diverted to the side reaction forming malate. 

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