scholarly journals The regulation of glucose and pyruvate formation from glutamine and citric-acid-cycle intermediates in the kidney cortex of rats, dogs, rabbits and guinea pigs

1980 ◽  
Vol 188 (3) ◽  
pp. 741-748 ◽  
Author(s):  
M Watford ◽  
P Vinay ◽  
G Lemieux ◽  
A Gougoux
Keyword(s):  
Citric Acid ◽  
Guinea Pig ◽  
Guinea Pigs ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Alternative Pathway ◽  
Lactate Production ◽  
Kidney Cortex ◽  
Acid Cycle ◽  
Pig Kidney

The suppression by 3-mercaptopicolinate of gluconeogenesis from glutamine or 2-oxoglutarate in rat or dog kidney tubules did not affect the amount of these substrates undergoing complete oxidation. Furthermore, 3-mercaptopicolinate caused an accumulation of lactate in dog tubules. 3-Mercaptopicolinate abolished both gluconeogenesis and substrate oxidation in tubules from rabbit and guinea-pig kidney. These results imply the presence of an alternative pathway to phosphoenolpyruvate carboxykinase/pyruvate kinase for the production of pyruvate from citric-acid-cycle intermediates in the kidney cortex of rats and dogs but not in that of rabbits or guinea pigs. Oxaloacetate decarboxylase (present in the kidney cortex of all four species) or ‘malic’ enzyme (present in rat and dog but absent in rabbit and guinea-pig kidney cortex) could function in this role. Our observations indicate that ‘malic’ enzyme is probably implicated in this phenomenon. The lactate production observed in dog tubules in the presence of 3-mercaptopicolinate can be suppressed when aspartate formation is inhibited by 2-amino-4-methoxy-trans-but-3-enoic acid. This suggests that the provision of cytosolic NADH from citric-acid-cycle intermediates is facilitated by accumulation of aspartate acting as a ‘sink’ for cytosolic oxaloacetate.

The Formation of Pyruvate from Citric Acid-Cycle Intermediates in Kidney Cortex

1979 ◽  
Vol 7 (4) ◽  
pp. 753-755 ◽  
Author(s):  
MALCOLM WATFORD ◽  
PATRICK VINAY ◽  
GUY LEMIEUX ◽  
ANDRÉ GOUGOUX
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Kidney Cortex ◽  
Acid Cycle

scholarly journals Functions of the Membrane-Associated and Cytoplasmic Malate Dehydrogenases in the Citric Acid Cycle ofEscherichia coli

2000 ◽  
Vol 182 (24) ◽  
pp. 6892-6899 ◽  
Author(s):  
Michel E. van der Rest ◽  
Christian Frank ◽  
Douwe Molenaar
Keyword(s):  
Citric Acid ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Wild Type ◽  
Batch Cultures ◽  
Acid Cycle ◽  
E Coli ◽  
Link Type ◽  
Phosphoenolpyruvate Synthase ◽  
Rates Of Growth

ABSTRACT Oxidation of malate to oxaloacetate in Escherichia colican be catalyzed by two enzymes: the well-known NAD-dependent malate dehydrogenase (MDH; EC 1.1.1.37 ) and the membrane-associated malate:quinone-oxidoreductase (MQO; EC 1.1.99.16 ), encoded by the genemqo (previously called yojH). Expression of themqo gene and, consequently, MQO activity are regulated by carbon and energy source for growth. In batch cultures, MQO activity was highest during exponential growth and decreased sharply after onset of the stationary phase. Experiments with the β-galactosidase reporter fused to the promoter of the mqo gene indicate that its transcription is regulated by the ArcA-ArcB two-component system. In contrast to earlier reports, MDH did not repressmqo expression. On the contrary, MQO and MDH are active at the same time in E. coli. For Corynebacterium glutamicum, it was found that MQO is the principal enzyme catalyzing the oxidation of malate to oxaloacetate. These observations justified a reinvestigation of the roles of MDH and MQO in the citric acid cycle of E. coli. In this organism, a defined deletion of the mdh gene led to severely decreased rates of growth on several substrates. Deletion of the mqo gene did not produce a distinguishable effect on the growth rate, nor did it affect the fitness of the organism in competition with the wild type. To investigate whether in an mqo mutant the conversion of malate to oxaloacetate could have been taken over by a bypass route via malic enzyme, phosphoenolpyruvate synthase, and phosphenolpyruvate carboxylase, deletion mutants of the malic enzyme genessfcA and b2463 (coding for EC 1.1.1.38 and EC1.1.1.40 , respectively) and of the phosphoenolpyruvate synthase (EC2.7.9.2 ) gene pps were created. They were introduced separately or together with the deletion of mqo. These studies did not reveal a significant role for MQO in malate oxidation in wild-type E. coli. However, comparing growth of themdh single mutant to that of the double mutant containingmdh and mqo deletions did indicate that MQO partly takes over the function of MDH in an mdh mutant.

Differences between mouse and rat pancreatic islets: succinate responsiveness, malic enzyme, and anaplerosis

2002 ◽  
Vol 283 (2) ◽  
pp. E302-E310 ◽  
Author(s):  
Michael J. MacDonald
Keyword(s):  
Citric Acid ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Rat Islets ◽  
Rat Pancreatic Islets ◽  
Mouse Islets

Succinic acid methyl esters are potent insulin secretagogues in rat pancreatic islets, but they do not stimulate insulin release in mouse islets. Unlike rat and human islets, mouse islets lack malic enzyme and, therefore, are unable to form pyruvate from succinate-derived malate for net synthesis of acetyl-CoA. Dimethyl-[2,3-14C]succinate is metabolized in the citric acid cycle in mouse islets to the same extent as in rat islets, indicating that endogenous acetyl-CoA condenses with oxaloacetate derived from succinate. However, without malic enzyme, the net synthesis from succinate of the citric acid cycle intermediates citrate, isocitrate, and α-ketoglutarate cannot occur. Glucose and other nutrients that augment α-ketoglutarate formation are secretagogues in mouse islets with potencies similar to those in rat islets. All cycle intermediates can be net-synthesized from α-ketoglutarate. Rotenone, an inhibitor of site I of the electron transport chain, inhibits methyl succinate-induced insulin release in rat islets even though succinate oxidation forms ATP at sites II and III of the respiratory chain. Thus generating ATP, NADH, and anaplerosis of succinyl-CoA plus the four-carbon dicarboxylic acids of the cycle and its metabolism in the citric acid cycle is insufficient for a fuel to be insulinotropic; it must additionally promote anaplerosis of α-ketoglutarate or two intermediates interconvertible with α-ketoglutarate, citrate, and isocitrate.

scholarly journals Malate : Quinone Oxidoreductase and Malic Enzyme are required for the Plant Pathogen Pseudomonas syringae pv. tomato DC3000 to Utilize Malate

2016 ◽  
Vol 13 (2) ◽  
Author(s):  
Zabrina Ebert ◽  
Preston Jacob ◽  
Katrina Jose ◽  
Lina Fouad ◽  
Katherine Vercellino ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Citric Acid ◽  
Pseudomonas Syringae ◽  
Plant Pathogen ◽  
Malic Enzyme ◽  
Citric Acid Cycle ◽  
Wild Type ◽  
In Planta ◽  
Quinone Oxidoreductase ◽  
Acid Cycle

Pseudomonas syringae pv. tomato strain DC3000 (DC3000) is a gram-negative bacterial plant pathogen that causes disease on tomato and the model plant Arabidopsis thaliana. Interestingly, previous studies showed that malate:quinone oxidoreductase (Mqo), an enzyme in the citric acid cycle, is required for DC3000 to cause disease on these plants. In addition, growth of DC3000 lacking the mqo gene in minimal medium with malate was significantly delayed, but eventually reached wild-type levels of growth, which is similar to growth in planta. This suggests that malate may be an important carbon source for DC3000. One reason the mqo::KO bacteria may be able to reach wild-type levels of growth in culture and plants is that the DC3000 malic enzyme may be used to complete the citric acid cycle. Our research shows that a mutant strain lacking a functional mqo gene and malic enzyme gene (mqo::KO;ME::pJP) fails to grow in minimal media cultures with malate and has reduced growth in media with citrate, indicating that both Mqo and ME are required for normal growth when utilizing these carbon sources. Future studies looking at growth of this double mutant in plants will identify how important the activities of both of these genes are for DC3000 to cause disease in plants. KEY WORDS: Malate:quinone Oxidoreductase; Malic Enzyme; MQO; Pseudomonas syringae; Arabidopsis thaliana; Malate; Citrate; DC3000

scholarly journals Conversion of glutamate into aspartate in guinea-pig cerebral-cortex slices

1968 ◽  
Vol 107 (1) ◽  
pp. 109-111 ◽  
Author(s):  
Gerald Simon ◽  
M. M. Cohen ◽  
J. F. Berry
Keyword(s):  
Cerebral Cortex ◽  
Amino Acid ◽  
Citric Acid ◽  
Guinea Pig ◽  
Amino Acid Metabolism ◽  
Citric Acid Cycle ◽  
Acid Metabolism ◽  
Acid Cycle ◽  
Cortex Slices

1. When guinea-pig cerebral-cortex slices were incubated with [U−14C]glutamate as substrate, the specific radioactivities of the citric acid-cycle intermediates were lower than that of the aspartate isolated from the same vessels. 2. Aspartate was significantly labelled when [5−14C]glutamate was used as substrate and the aspartate contained almost no label when [1−14C]glutamate was present as substrate. 3. When specifically labelled glutamate was used as substrate, the label was found in the isolated aspartate in the position that would be predicted by citric acid-cycle mechanisms. 4. The results are consistent with the theory of ‘compartmentation’ of amino acid metabolism.

EFFECT OF SERUM GONADOTROPHIN ON DEHYDROGENASES OF THE CITRIC ACID CYCLE IN THE OVARY OF THE RAT

1963 ◽  
Vol 42 (4) ◽  
pp. 480-484 ◽  
Author(s):  
B. Eckstein ◽  
R. Landsberg
Keyword(s):  
Citric Acid ◽  
Citric Acid Cycle ◽  
Age Groups ◽  
Succinic Dehydrogenase ◽  
Immature Rat ◽  
Acid Cycle ◽  
Immature Rats ◽  
Rat Ovary

ABSTRACT The succinic, malic and isocitric dehydrogenases in the ovary of immature and mature, normal and serum gonadotrophin injected rats were examined. The Qo2 of these enzymes were markedly enhanced in the gonadotrophin injected rats of both age groups, except in the case of succinic dehydrogenase in the ovary of the immature rats, where a slight non-significant decrease was noted. It is concluded that in the mature rat ovary, gonadotrophin administration stimulates the activity of all the examined dehydrogenases of the citric acid cycle, whereas in the immature rat ovary, at least the isocitric- and malic dehydrogenases are thus stimulated.

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