Succinic Acid Production by Rumen Bacteria. III. Enzymic Studies on the Formation of Succinate by Ruminococcus Flavefaciens

Abstract

SummaryEnzymes involved in succinic acid production by strain C of R. ftavefacien8 were investigated in cell-free extracts. The results indicate that phosphoenolpyruvate is carboxylated by a phosphoenolpyruvate carboxykinase which uses GDP as phosphate acceptor, and that the oxaloacetate so formed is converted to succinate via a DPNH-dependent malate dehydrogenase, a fumarate hydratase, and a DPNHdependent fumarate reductase. Succinate dehydrogenase activity was also observed which differed markedly from fumarate reductase in that DPN+ was not reduced and in inhibition characteristics.There is no evidence that synthesis of ATP is associated with the conversion of oxaloacetate to succinate, or that DPNH oxidation is coupled to ATP synthesis. It is concluded that approximately 2·8 moles of ATP are formed per mole of glucose fermented by this organism.

Enzymes of Pyruvate and Phosphoenolpyruvate Carboxylation in Rumen Bacteria

“…pH 7-7.5 (little activity at pH 6) and metal ion activation (Mn'. ) Mg-t), were similar to those reported by Hopgood and Walker (1969).…”

“…has been found to be widely distributed in plant tissues (Walker 1962) and in microorganisms (Canovas and Kornberg 1965). Hopgood and Walker (1969) showed the occurrence of carboxylation of PEP in extracts of the rumen isolate R. flavefaciens. They suggested the reaction presented in equation 3.…”

Microbial Cellulose Utilization: Fundamentals and Biotechnology

“…The ruminal species F. succinogenes and R. flavefaciens produce large amounts of succinate, which in the rumen is converted by other bacteria to propionate, a gluconeogenic substrate for the ruminant host. Succinate production occurs via net fixation of CO 2 by PEP carboxykinase, with subsequent conversion of oxaloacetate to malate and succinate (283,448,619). Lactate, produced in large amounts by many rapidly growing saccharolytic anaerobes, is generally not a major fermentation product in cellulolytic anaerobes, which have relatively low growth rates even on soluble sugars (207,619).…”

Production of Enzymes Degrading Plant Cell Walls and Fermentation of Cellobiose by Ruminococcus flavefaciens in Batch and Continuous Culture

“…For the purpose of calculating YATP it was assumed that a net yield of 2 mol ATP was obtained from the conversion of glucose to pyruvate via the Embden-Meyerhof-Parnas pathway and that 1 mol ATP was synthesized during the formation of acetate from pyruvate. Since, in R. Jlavefaciens, succinate arises via the formation of oxaloacetate from phosphoenolpyruvate (Hopgood & Walker, 1969), it is assumed that this would negate any ATP which might arise from subsequent electron transport phosphorylation associated with the reduction of fumarate to succinate (de Vries et al, 1973). The YATp calculated on this basis varied with nutrient limitation and growth rate between 10.81 and 16-39.…”