Summary: The activities of seven enzymes which catalyse reactions of the tricarboxylic acid cycle were assayed in extracts of five lactaphilic and five glycophilic strains of acetic acid bacteria. Except for isocitrate dehydrogenase (which was not detected in glycophilic extracts) all other enzymes were found in all strains; but in general these enzymes were much more abundant in the lactaphilic extracts. In particular, extracts of glycophiles possessed only feeble citrate synthase, aconitate hydratase, fumarate hydratase and l-malate dehydrogenase activities and only their 2-oxoglutarate and succinate dehydrogenase activities were comparable to the corresponding activities in extracts of lactaphiles. Oxaloacetate decarboxylase activity was also greater in lactaphiles than in glycophiles. Two enzymes which oxidized l-malate were found: that in was an NADP-linked dehydrogenase, while the other more generally distributed enzyme required no added co-factors and may be cytochrome-linked. The evidence indicates that the tricarboxylic acid cycle may make a greater quantitative contribution to the metabolism of lactaphilic than to that of glycophilic organisms.


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