Further enzyme histochemical observations on the segmentation of the proximal tubules in the kidney of the male rat.
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Isocitrate dehydrogenase
Malate dehydrogenase
Oxoglutarate dehydrogenase complex
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The isolation is described of pure cultures of three non-methane-utilizing methylotrophic bacteria which, together with the previously described Bacillus PM6, have a very limited range of growth substrates; these organisms are designated “restricted facultative’ methylotrophs. Two of these isolates, W6A and W3A1, grow only on glucose out of 50 non-C1 compounds tested, whereas the third isolate S2A1 and Bacillus PM6 grow on betaine, glucose, gluconate, alanine, glutamate, citrate and nutrient agar, but not on any of a further 56 non-C1 compounds. Crude sonic extracts of trimethylamine-grown and glucose-grown W6A and W3A1 isolates, and of trimethylamine-grown C2A1 (an obligate methylotroph) contain (i) no detectable 2-oxogltarate dehydrogenase activity, (ii) very low or zero specific activities of succinate dehydrogenase and succinyl-CoA synthetase and (iii) NAD+-dependent isocitrate dehydrogenase activity. Extracts of trimethylamine-grown PM6 and S2A1 methylotrophs have (i) very low 2-oxoglutarate dehydrogenase specific activities, (ii) comparatively high specific activities of succinate dehydrogenase, malate dehydrogenase and succinyl-CoA synthetase and (iii) NADP+-dependent isocitrate dehydrogenase activity but no NAD+-dependent isocitrate dehydrogenase activity. The activities of most of these enzymes are increased during growth on glucose, alanine, glutamate or citrate, but only very low 2-oxoglutarate dehydrogenase activities are present under all growth conditions. The restricted facultative methylotrophs grow on certain non-C1 compounds in the absence of 2-oxoglutarate dehydrogenase and, in some cases, of other enzymes of the tricarboxylic acid cycle; these lesions cannot therefore be the sole cause of obligate methylotrophy.
Methylotroph
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Oxoglutarate dehydrogenase complex
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Isocitrate dehydrogenase
Malate dehydrogenase
Oxoglutarate dehydrogenase complex
Phosphogluconate dehydrogenase
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The regulation of alpha-ketogluterate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase, and malic enzyme has been studied in Bacillus subitilis. The levels of these enzymes increase rapidly during late exponential phase in a complex medium and are maximal 1 to 2 h after the onset of sporulation. Regulation of enzyme synthesis has been studied in the wild type and different citric acid cycle mutants by adding various metabolites to the growth medium. Alpha-ketoglutarate dehydrogenase is induced by glutamate or alpha-ketoglutarate; succinate dehydrogenase is repressed by malate; and fumarase and malic enzyme are induced by fumarate and malate, respectively. The addition of glucose leads to repression of the citric acid cycle enzymes whereas the level of malic enzyme is unaffected. Studies on the control of enzyme activities in vitro have shown that alpha-ketoglutarate dehydrogenase and succinate dehydrogenase are inhibited by oxalacetate. Enzyme activities are also influenced by the energy level, expressed as the energy charge of the adenylate pool. Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, and malic enzyme are inhibited at high energy charge values, whereas malate dehydrogenase is inhibited at low energy charge. A survey of the regulation of the citric acid cycle in B.subtilis, based on the present work and previously reported results, is presented and discussed.
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Oxoglutarate dehydrogenase complex
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SUMMARYA number of morphological and reproductive similarities between members of the genus Dictyuchus and those of Achlya prompted the present study of enzyme activities of Dictyuchus monosporus. Specific activities of phosphofructokinase, aldolase, isocitrate dehydrogenase, malate dehydrogenase, cytochrome oxidase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, lactate dehydrogenase, alcohol dehydrogenase, and catalase in Dictyuchus were determined. The activities found were in general comparable to those found in Achlya ambisexualis, with the exceptions of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, whose activities were considerably lower in Dictyuchus.
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We studied the physiological function of alpha-ketoglutarate dehydrogenase complex (KGDH) on the metabolism of Torulopsis glabrata.With manipulation of KGDH in Torulopsis glabrata, we screened a mutant strain T. glabrata kgd1:: kan, in which the kgd1 gene encoding the E1 subunit of KGDH was deleted.Disruption of KGDH resulted in: (a) the enhancement of glyoxalate pathway as a complementarity for carbon metabolism in TCA cycle; (b) compared with that of the control, the ratio of NADH/NAD + and ATP/ADP decreased by 33.7% and 31.8%, respectively. But the specific activities of pyruvate dehydrogenase, isocitrate dehydrogenase and malate dehydrogenase increased by 58.1%, 33.3% and 32.5%, respectively; (c) the intracellular concentration of pyruvate was reduced by 49.9%, while the intracellular concentration of succinate, malate and alpha-ketoglutarate was higher 172.7%, 66.1% and 41.1% than the corresponding values of the control; (d) The content of pyruvate-family amino acid was 29.3% lower while the level of glutamate-family amino acid and aspartate-family amino acid were 34.7% and 26.8% higher than that of control.Those results present here demonstrated that alpha-ketoglutarate dehydrogenase complex plays essential role on the metabolism of yeast.
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Lipoic acid (lip) and 2-oxoglutarate dehydrogenase (sucA) mutants of Escherichia coli k12 exhibit a requirement for exogenous succinate during aerobic growth on glucose minimal medium. Reversion studies have shown that this requirement can be suppressed by gal-linked mutations which inactivate succinate dehydrogenase. Biochemical and genetic studies confirmed that the succinate dehydrogenase gene (sdh) is affected and that suppression is mediated by the same intergenic and indirect mechanism that generates succinate independence in partial revertants of lipoamide dehydrogenase mutants ( Creaghan & Guest, 1977 ). A series of isogenic strains containing all combinations of mutations affecting 2-oxoglutarate dehydrogenase (sucA), succinate dehydrogenase (sdh), isocitrate lyase (aceA) and fumarate reductase (frd) in a background lacking succinate semialdehyde dehydrogenase, was constructed to assess the importance of these enzymes as sources of endogenous succinate (succinyl-CoA) during aerobic and anaerobic growth on glucose. Only strains combining a deficiency in 2-oxoglutarate dehydrogenase with the presence of an active succinate dehydrogenase required succinate for aerobic growth. In all mutants, including the triple mutant (frd sucA aceA), the succinate requirement was suppressed by inactivating succinate dehydrogenase. The aerobic growth rates of succinate-independent strains were most affected by lack of isocitrate lyase but only two mutants (sdh sucA aceA and frd sdh sucA aceA) grew faster with added succinate: the growth yields were lowered by deficiencies in isocitrate lyase and also succinate dehydrogenase. It is concluded that very little succinate is needed for biosynthesis during aerobic growth on glucose and the requirement for relatively high concentrations of succinate (2 mm) by mutants lacking 2-oxoglutarate dehydrogenase or related functions stems from the presence of active succinate dehydrogenase. Anaerobically, either isocitrate lyase or fumarate reductase is essential for succinate-independent growth on glucose.
Isocitrate dehydrogenase
Fumarate reductase
Oxoglutarate dehydrogenase complex
Malate dehydrogenase
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Fumarase
Isocitrate dehydrogenase
Malate dehydrogenase
Oxoglutarate dehydrogenase complex
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Isocitrate dehydrogenase
Malate dehydrogenase
Malic enzyme
Oxoglutarate dehydrogenase complex
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The regulatory properties of NAD(+)-isocitrate dehydrogenase and oxoglutarate dehydrogenase in extracts of yeast and rat heart mitochondria were studied under identical conditions. Yeast NAD(+)-isocitrate dehydrogenase exhibits a low K0.5 for isocitrate and is activated by AMP and ADP, but is insensitive to ATP and Ca2+. In contrast, the rat heart NAD(+)-isocitrate dehydrogenase was insensitive to AMP, but was activated by ADP and by Ca2+ in the presence of ADP or ATP. Both yeast and rat heart oxoglutarate dehydrogenase were stimulated by ADP, but only the heart enzyme was activated by Ca2+. All the enzymes studied were activated by decreases in pH, but to differing extents. The effects of Ca2+, adenine nucleotides and pH were through K0.5 for isocitrate or 2-oxoglutarate. These observations are discussed with reference to the deduced amino acid sequences of the constituent subunits of the enzymes, where they are available.
Isocitrate dehydrogenase
Oxoglutarate dehydrogenase complex
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