Carbon assimilation by Pseudomonas oxalaticus (OXI). 4. Metabolism of oxalate in cell-free extracts of the organism grown on oxalate

Abstract

The oxidation level of oxalate is such that incorporation of its carbon into cell constituents must involve a net reduction. If it is the sole carbon source for microbial growth then it must also undergo condensation reactions resulting in the synthesis of, for example, C3 and C4 units necessary for formation of carbohydrate and amino acid carbon skeletons (for a review of this aspect, see Kornberg, 1959). Previous work, mainly with whole cells of P8eudomona8 oxalaticus (Quayle & Keech, 1959a, 1960) indicated that a reductive step precedes any condensation reactions, and that this initial reduction reaction is that of oxalylcoenzyme A to glyoxylate. It was also suggested that successive steps involve condensation of two molecules of the glyoxylate to tartronic acid semialdehyde, which in turn is reduced to glyceric acid by a reaction sequence similar to that proposed for the growth of Pseudomona8 species on glycollate (Kornberg & Gotto, 1959). The formation and metabolism of oxalylcoenzyme A, including its reduction to glyoxylate by reduced triphosphopyridine nucleotide in cellfree extracts of P. oxalaticus, are reported in this paper. Part of this work has been presented to the Biochemical Society (Quayle, Keech & Taylor, 1960). METHODS AND MATERIA:LS Maintenance and growth of the organism. The growth conditions have been described by Quayle & Keech (1960). Isotopic materials. Radioactive chemicals were purchased from The Radiochemical Centre, Amersham, Bucks.

Purification and characterization of oxalyl-coenzyme A decarboxylase from Oxalobacter formigenes

“…Cell extracts degrade oxalate to CO2 and formate but require an acyl coenzyme A (CoA) for activity. In this respect, 0. formigenes extracts are similar to Pseudomonas oxalaticus extracts (11,(13)(14)(15), which also require oxalylCoA. Oxalate metabolism by O. formigenes differs from that of the aerobic P. oxalaticus because formate is an end product of the anaerobic metabolism by 0. formigenes, whereas P. oxalaticus oxidizes formate to CO2 via a NADlinked formate dehydrogenase (15).…”

Oxalyl-Coenzyme A Reduction to Glyoxylate Is the Preferred Route of Oxalate Assimilation in Methylobacterium extorquens AM1

“…O. formigenes was found in the human gut and those of other warm-blooded animals (3), and its presence is known to inhibit the formation of kidney stones (2,60). C. oxalaticus was isolated from the intestine of an Indian earthworm (32), and its oxalate metabolism was investigated by Quayle and coworkers in the 1960s (48)(49)(50)(51)(52)(53)(54). The two organisms convert oxalate to formate by using oxalyl-coenzyme A (oxalyl-CoA) decarboxylase and formyl-CoA transferase; both enzymes have been previously characterized and identified (6, 6a, 42, 48, 49, 61, 65).…”

“…Although C. oxalaticus is able to oxidize formate to carbon dioxide with the generation of redox equivalents (51), it remains unclear how the generation of reductant is accomplished in the anaerobe O. formigenes (20). Both organisms use the glycolate pathway for the assimilation of oxalate into biomass (21,53,55), a pathway that is also referred to as the glycerate pathway (20). By this pathway, oxalate is reduced to glyoxylate and then converted into glycerate by glyoxylate carboligase and tartronic semialdehyde reductase.…”

The Assimilation of 2-C Compounds other than Acetate

“…Pseudomonas oxalaticus also formed these enzymes during growth on oxalate ; this provided evidence for the initial reduction of oxalate to glyoxylate by this organism (Quayle & Keech, 1959). In this process oxalate is activated to oxalylcoenzyme A (Quayle, Keech & Taylor, 1961) which is reduced to glyoxylate by glyoxylic dehydrogenase and NADPH, . Thus pseudomonads growing on glycollate, glycine or oxalate are all in effect growing on glyoxylate and a source of ' reducing power 'I.…”