Pyrrole-2-carboxylate decarboxylase enzyme

Also interesting is the synthesis of pyrrole-2-carboxylate from carbon dioxide and pyrrole using reverse reaction of pyrrole-2-carboxylate decarboxylase enzyme... 

Pyrrole-2-carboxylate decarboxylase attains equilibrium in the course of either decarboxylation or carboxylation (Fig. 8). The decarboxylation of 100 mM pyrrole-2-carboxylate was in equilibrium after Ih, resulting in an equilibrium constant of 0.3 M." Due to this balanced equilibrium, the enzyme also catalyzed the reverse carboxylation of pyrrole after the addition of HCO3, leading to a similar equilibrium constant of 0.4 M and a shift of the [pyrrole]/[pyrrole-2-carboxylate] ratio toward the acid. 

The enzymes catalyzing the Kolbe-Schmitt carboxylation seem to occur ubiquitously. Some of them, such as 2,6-dihydroxybenzoate decarboxylase and pyrrole-2-carboxylate decarboxylase, catalyze efficiently the reverse carboxylation reaction and accumulate high concentration of 2,6-dihydroxybenzoate from 1,3-dihydroxybenzene and pyrrole-2-carboxylate from pyrrole, respectively, in the... 

Wieser M, Yoshida T, Nagasawa T (2001) Carbon dioxide fixation by reversible pyrrole-2-carboxylate decarboxylase and its application. J Mol Catal B Enzym 11 179-184... 

Omura H, Wieser M, Nagasawa T (1998) Pyrrole-2-carboxylate decarboxylase from Bacillus megaterium PYR2910, an organic-acid-requtring enzyme. Em J Biochem 253 480-484... 

We have presented evidence that pyrrole-2-carboxylic acid decarboxylates in acid via the addition of water to the carboxyl group, rather than by direct formation of C02.73 This leads to the formation of the conjugate acid of carbonic acid, C(OH)3+, which rapidly dissociates into protonated water and carbon dioxide (Scheme 9). The pKA for protonation of the a-carbon acid of pyrrole is —3.8.74 Although this mechanism of decarboxylation is more complex than the typical dissociative mechanism generating carbon dioxide, the weak carbanion formed will be a poor nucleophile and will not be subject to internal return. However, this leads to a point of interest, in that an enzyme catalyzes the decarboxylation and carboxylation of pyrrole-2-carboxylic acid and pyrrole respectively.75 In the decarboxylation reaction, unlike the case of 2-ketoacids, the enzyme cannot access the potential catalysis available from preventing the internal return from a highly basic carbanion, which could be the reason that the rates of decarboxylation are more comparable to those in solution. Therefore, the enzyme cannot achieve further acceleration of decarboxylation. In the carboxylation of pyrrole, the absence of a reactive carbanion will also make the reaction more difficult however, in this case it occurs more readily than with other aromatic acid decarboxylases. 

Carboxylation of organic molecules using CO2 has received attention as an environmentally benign synthetic method. A decarboxylase, an enzyme from Bacillus megaterium that catalyzes the elimination of CO2 from organic molecules, has been found to also catalyze the reverse CO2 fixation reactions. " The substrate scope of this enzyme, however, is limited to pyrrole, which is carboxylated to form pyrrole-2-carboxylate (Fig. 10.41(a)). For the carboxylations of phenol and catechol, decarboxylases from Clostridium hydroxybenzoicum have been isolated and employed (Fig. 41(b) and(c)). ... 

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