抄録
Many of the putative enzymes mediating oxidative reactions of the citric acid cycle were measured in cell-free extracts of Lactobacillus plantarum ATCC 8014, L. casei ATCC 7469, L. helveticus ATCC 15009, and L. acidophilus ATCC 11506. The activities of citrate synthase and aconitase were demonstrated in all the strains investigated. None of isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase, and succinate dehydrogenase activities were detected in any of the strains tested. Fumarase and malate dehydrogenase activities could be detected in some but not all of the strains. On the other hand, all the strains had the activities of fumarase and malate dehydragenase when measured in the direction of reductive reactions of the cycle. In addition, the activities of fumarate reductase and citrate lyase were found in all the strains and in most strains, respectively. All these results suggest that the oxidative pathway in the citric acid cycle serving both bioenergetic and 2-oxoglutarate biosynthetic functions is completely inoperative in lactobacilli, while a set of reversed reactions leading to succinate synthesis functions in these bacteria. These findings also suggest that the lack of 2-oxoglutarate dehydrogenase activities is closely related to the inability to synthesize glutamate in lactobacilli.
