Phosphoenolpyruvate carboxytransphosphorylase

This enzyme [EC 4.1.1.38] (also known as phosphoenolpyruvate carboxytransphosphorylase, phosphopyruvate carboxylase, and phosphoenolpyruvate carboxylase) catalyzes the reaction of phosphoenolpyruvate with orthophosphate and carbon dioxide to produce oxaloacetate and pyrophosphate (or diphosphate). The enzyme also catalyzes the reaction of phosphoenolpyruvate with orthophosphate to produce pyruvate and pyrophosphate. 

Phosphoenolpyruvate.—Phosphoenolpyruvate carboxytransphosphorylase catalyses two separate conversions of phosphoenolpyruvate (6) (Scheme 3). In the absence of carbon dioxide pyruvate and inorganic pyrophosphate may be formed enzymic dephosphorylation of (6) to enolpyruvate is probably followed by the non-enzymic protonation of the latter giving rise to pyruvate. 

Davis JJ, Willard JM and Wood HG (1969) Phosphoenolpyruvate carboxytransphosphorylase. ni. Comparison of the fixation of carbon dioxide and the conversion of phosphoenolpyruvate and phosphate into pyruvate and pyrophosphate. Biochemistry 8 3127-3136... 

Silverman M and Werkman CH (1939) Adaptation of the propionic acid bacteria to vitamin Bi synthesis including method of assay. J Bacteriol 38 25-32 Siu PML and Wood HG (1962) Phosphoenolpyruvic carboxytransphosphorylase, a CO2 fixation enzyme from propionic acid bacteria. J Biol Chem 237 3044-3051 Sizova AV and Arkadjeva ZA (1968) Propionic acid bacteria of rumen and their capacity for vitamin B12 biosynthesis. Mikrobiol Sintez 10 8-13... 

Cooper TG, Tchen TT, Wood HG, Benedict CR. (1968). The carboxylation of phospho-enolpyruvate and pyruvate. I. The active species of COj utilized by phosphoenolpyruvate carboxykinase, carboxytransphosphorylase, and pyruvate carboxylase. J Biol Chem, 243, 3857-3863. 

Reaction 3.1, the key reaction of propionic acid fermentation, is catalyzed by pyruvate carboxytransphosphorylase, a unique biotin-dependent transcarboxylase (see below). There are other reactions of carboxyl group transfer catalyzed by phosphoenolpyruvate (PEP) carboxytransphosphorylase and phosphoenolpyruvate carboxykinase, but these (i) do not require biotin and (ii) use CO2 as the source of carboxyl groups. The actual species involved may be HCO3" (or H2CO3) rather than free CO2 (Cooper et al., 1968), since free CO2 is not evolved in the PEP carboxytransphosphorylase reaction (Swick and Wood, 1960). Propionic acid bacteria are able to decarboxylate succinate, producing CO2 in a biotin-dependent reaction (Delwiche,1948 Lichstein, 1958). If succinate is accumulated as the end product, then the cycle (see Fig. 3.1) is broken, and oxaloacetic acid is not supplied by reaction 3.1, but is formed primarily by CO2 fixation onto PEP catalyzed by PEP carboxytransphosphorylase (PEP-CTP). 

The reaction of CO2 fixation onto phosphoenolpyruvic acid by PEP carboxytransphosphorylase is considered (O Brien and Wood, 1974) as a control mechanism of propionic acid fermentation. They observed a conversion of the enzymatically active tetrameric form of PEP carboxytransphosphorylase isolated from P. shermanii into a less active dimeric form induced by oxalate, malate and fumarate. Therefore, the loss of activity by enzyme dissociation, accompanied by increased proteolysis, is an effective means of controlling the level of intermediates in propionic acid fermentation. Differential abilities of propionibacteria to fix CO2 could be associated (Wood and Leaver, 1953) with their abilities to carry out the reaction C02 Ci and to form sulfhydryl complexes with Ci. 

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