Enzymes of the Tricarboxylic Acid Cycle in Acetic Acid Bacteria

Abstract

The activities of seven enzymes which catalyze 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 Acetobacter acidum-mucosum was a nicotinamide-adenine-dinucleotide-phosphate (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.