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.

Strain C of R. flavejaciens ferments [1_14C]glucose with the production of methyl-labelled succinic and acetic acids, and the specific activity of the succinic acid produced is one-half that of the substrate. Fermentation of glucose in the presence of [14C]bicarbonate gives rise to carboxyl-labelled succinic acid. Formic acid is also labelled, either by direct exchange with 14C02 or by exchange of 14C02 with the carboxyl group of pyruvate. These results are compatible with the formation of succinate from glucose via the Embden-Meyerhof pathway and carboxylation of pyruvate or phosphoenolpyruvate.

A strain of R. flavefaciens was isolated from the sheep rumen. Succinic acid was a major end� product of glucose fermentation by this organism when C02 was freely available, but in the absence of C02, the fermentation was nearly homolactic. The products of pyruvate fermentation were consistent with the proposition that pyruvate is an intermediate in the fermentation of glucose. Possible routes of the fermentation are discussed in the light of these findings.

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An enzyme hydrolyzing a largely insoluble preparation of hemicellulose from wheaten hay was purified from sheep rumen microflora. The enzyme catalysed the hydrolysis of hemicellulose to xylose, xylobiose, xylotriose, and higher oligosaccharides together with glucose and arabinose. Enzyme activity was rapidly destroyed by heating at temperatures above 40� and by raising the pH above the optimum of 6.0. Purified enzyme preparations did not hydrolyse starch or cellulose. A partial inhibition of hemicellulase activity was observed in the presence of p-chloromercuribenzoate.