The Role of Transcarboxylation in Propionic Acid Fermentation

Abstract

BIOCHEMISTRY: SWICK AND WOOD PROC. N. A. S. sumption that the structure of prodigiosin is correctly represented in Figure 1. Furthermore, inspection of the prodigiosin molecule suggests that at least the methoxyl-bearing ring may be derived directly from hydroxy-proline.Summary.-Glycine-2-C 4 was incorporated into prodigiosin, the red pigment of Serratia marcescens, in confirmation of the results of Hubbard and Rimington. 5-Aminolevulinic acid-5-C'4 was, however, not incorporated showing that the 3 pyrrole rings of prodigiosin must be derived from a precursor other than porphobilinogen, the pyrrolic precursor of porphyrins. Experiments with L-proline-C'4 indicated that proline or a closely related metabolic derivative is a precursor of prodigiosin.The evidence that propionibacteria form propionate by the direct decarboxylation of succinyl CoAl has been reviewed by Wood et al.2 It has generally been considered that carbohydrates, e.g., glucose, glycerol, etc. are catabolized to pyruvate which is then converted to oxalacetate by the fixation of carbon dioxide. Oxalacetate is reduced to succinate, which in turn is esterified with CoA and decarboxylated to propionyl CoA and CO2. Therefore the reduction of one mole of pyruvate to propionate would be expected to involve the fixation and release of one mole of CO2.

Pathway of propionate formation from ethanol in Pelobacter propionicus

“…The organism combines this carboxylation with methylmalonyl CoA decarboxylation in an almost energy-neutral reaction catalyzed by a transcarboxylase. Similar transcarboxylases have been found in the classical propionibacteria (Swick and Wood 1960;Wood 1972), in Arachnia propionica (Allen and Linehan 1977) and in Desulfobulbus propionieus (Stams et al 1984). Pelobacter propionieus also links succinate activation to succinyl CoA with propionate formation from propionyl CoA in a CoA transferase reaction.…”

“…Succinate is rearranged via its CoA derivative to methylmalonyl CoA which is decarboxylated and eventually yields propionate (see e.g. Swick and Wood 1960;Allen et al 1964;Galivan and Allen 1968;de Vries et al 1977b; Thompson et al 1984). A few other strict anaerobes such as Megasphaera elsdenii, Bacteroides ruminicola, and Clostridium propionicum (Brockmann and Wood 1975; Offprint requests to: B. Schink Leaver et al 1955;Walln6fer and Baldwin 1967) form propionate via the acrylate pathway which, contrary to the succinate pathway, does not involve a symmetrical intermediate and, therefore, does not randomize the distribution of selectively labeled carbon atoms.…”

The Carboxylatin of Pyuvte by Biotin-Enzymes

“…This rather broad distribution of pyruvate carboxylase contrasts with that of transcar boxylase which has been found thus far only in the propionic acid bacteria (3).…”

The Biotin‐Dependent Enzymes

“…Exceptions to this are 8-methylcrotonyl CoA (80,110,111) and geranyl CoA (112) carboxylases, where the electrophilic site, hence the site of carboxylation, is displaced to the y-position by conjugation (Sections VI.C, V1.D). The second step ofthe transcarboxylase (113,114) reaction makes use of either an u-keto acid (reaction 3) or an acyl CoA derivative (reaction 2) as carboxyl acceptor, thereby completing the transcarboxylation sequence and generating a b-keto acid or malonyl CoA derivative, respectively. With the decarboxylases (115)(116)(117), it has not yet been established whether the second step (decarboxylation of enzyme-C02-, reaction 5 ) , involves water as the carboxyl acceptor or proceeds via a unimolecular decarboxylation reaction.…”