Showing papers on "Malic enzyme published in 1976"
TL;DR: Genetic analysis of 119 acetate non-utilizing (acu) mutants in Aspergillus nidulans revealed ten new loci affecting acetate metabolism in addition to the three previously recognized on the basis of resistance to fluoroacetate and acetateNon-utilization.
Abstract: Genetic analysis of 119 acetate non-utilizing (acu) mutants in Aspergillus nidulans revealed ten new loci affecting acetate metabolism in addition to the three previously recognized on the basis of resistance to fluoroacetate and acetate non-utilization. The enzyme lesions associated with mutations at seven of the acu loci are described. These are: facA (= acuA), acetyl-CoA synthase; acuD, isocitrate lyase; acuE, malate synthase; acuF, phosphoenolpyruvate carboxykinase; acuG, fructose 1,6-diphosphatase; acuK and acuM, malic enzyme. The acu loci have been mapped and are widely distributed over the genome of A. nidulans. Close linkage has only been found between acuA and acuD (less than 1% recombination). There is no evidence for any pleiotropic mutation in that region affecting the expression of both these genes. Poor induction of the enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase in mutants lacking acetyl-CoA synthase, and also in the other two classes of fluoroacetate-resistant mutants, indicates that the inducer, acetate, may be metabolized to a true metabolic inducer, perhaps acetyl-CoA, to effect formation of the enzymes. There is no evidence of any other class of pleiotropic recessive acu mutations affecting the expression of the acuD and acuE genes, which are therefore thought to be subject to negative rather than positive control.
186 citations
TL;DR: Glucagon rapidly and specifically inhibited synthesis of malic enzyme in preinduced cells, suggesting an action at the level of translation or cytoplasmic messenger RNA processing.
149 citations
TL;DR: It is proposed that NAD-malic enzyme in general supplements activity of NADP- malic enzyme present in these plants and may be specifically employed to increase internal concentrations of CO(2) for recycling during cessation of gas exchange in periods of severe drought.
Abstract: NAD-specific “malic” enzyme (EC 1.1.1.39) has been isolated and purified 1200-fold from leaves of Kalanchoe daigremontiana. Kinetic studies of this enzyme, which is activated 14-fold by CoA, acetyl-CoA, and SO42−, suggest allosteric properties. Cofactor requirements show an absolute specificity for NAD and for Mn2+, which cannot be replaced by NADP or Mg2+. For maintaining enzyme activity in crude leaf extracts a thiol reagent, Mn2+, and PVP-40 were required. The latter could be omitted from purified preparations. By sucrose density gradient centrifugation NAD-malic enzyme could be localized in mitochondria. A survey of plants with crassulacean acid metabolism revealed the presence of NAD-malic enzyme in all 31 plants tested. Substantial levels of this enzyme (121-186 μmole/hr·mg of Chl) were detected in all members tested of the family Crassulaceae. It is proposed that NAD-malic enzyme in general supplements activity of NADP-malic enzyme present in these plants and may be specifically employed to increase internal concentrations of CO2 for recycling during cessation of gas exchange in periods of severe drought.
80 citations
TL;DR: In this article, a half-site stoichiometry of two tight binding sites (KD=6 to 10 mum) per enzyme tetramer and at two to four weak binding sites was determined by EPR.
66 citations
TL;DR: The activities of citrate cleavage enzyme, fatty acid synthetase and malic enzyme in livers of rats fed the glycerol-containing diets were dramatically increased, however, this stimulation of enzyme activity occurred without a concomitant increase in the in vivo rate of fatty acid synthesis in the rat liver.
Abstract: The influence of glycerol on the rates of fatty acid snythesis in liver slices from rats and chickens in pieces of adipose tissue from rats was first studied. Then the effect of dietary glycerol on lipid metabolism in rats and cheickens was examined. Media containing 3 or 10 mM glycerol depressed the rate of glucose conversion to fatty acids in rat liver slices. However, media containing up to 25 mM glycerol did not influence the rate of fatty acid synthesis in chick liver slices. The inhibitory action of glycerol in rat liver slices might occur at the level of glucose (or glycogen) conversion to pyruvate because glycerol did not inhibit pyruvate or acetate conversion to fatty acids. Rats and chickens were fed glycerol containing diets for either 3 days or 3 weeks. Feeding diets containing 20.5 parts glycerol (22% of dietary energy) to rats or chickens did not influence the growth rate of the animals. However, substitution of 42.2 parts glycerol (43% of dietary energy) for glucose in the diet significantly depressed food intake and growth rate in both rats and chickens. The activities of citrate cleavage enzyme, fatty acid synthetase and malic enzyme in livers of rats fed the glycerol-containing diets were dramatically increased. However, this stimulation of enzyme activity occurred without a concomitant increase in the in vivo rate of fatty acid synthesis in the rat liver. In the chicken, unlike the rat, dietary glycerol did not stimulate but instead decreased hepatic malic enzyme and fatty acid synthetase activities. No significant differences in adipose tissue lipogenic enzyme activities or in the rates of fatty acid synthesis were observed in rats fed glycerol-containing diets. The lipogenic response to glycerol feeding depends on the species as well as the organ.
59 citations
TL;DR: Wild-type third instar larvae of Drosophilia melanogaster fed a casein-sucrose synthetic diet supplemented with phosphatidylcholine (4 mg/ml) possessed 33% more tissue lipid and a modified fatty acid profile compared to larvae fed a fat free-Sucrose diet.
Abstract: Wild-type third instar larvae of Drosophila melanogaster fed a casein-sucrose synthetic diet supplemented with phosphatidylcholine (4 mg/ml) possessed 33% more tissue lipid and a modified fatty acid profile compared to larvae fed a fat free-sucrose diet. The rates of lipid synthesis and pentose shunt activity were 2.1 and 2.2 times greater respectively in larvae fed the fat free-sucrose diet than in fat-sucrose fed animals. The tissue concentrations of acetyl-CoA and acytl-CoA were 80 and 61% higher respectively, CoA 49% lower, and the NADPH/NADP+ ratio greater in fat-sucrose fed larvae than in larvae fed a fat free-sucrose diet. Thus, larvae effectively utilized dietary lipid for lipid synthesis and as a supplementary energy source to carbohydrate. Larval oxidative NADP-enzyme tissue levels were dependent upon the interaction of at least three regulatory systems. Dietary carbohydrate induced high tissue levels of glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 6-phospho-gluconate dehydrogenase (EC 1.1.1.43), ostensibly via a glycolytic derivative. High tissue levels of malic enzyme (EC 1.1.1.40) and NADP-isocitrate dehydrogenase (EC 1.1.1.42) were induced by an acetate derivative postulated to be formed by the Krebs cycle. In contrast, a fatty acid derivative, presumably a product of β-oxidation, repressed the tissue levels of all four oxidative NADP-enzymes in larvae. A model of induction and repression regulatory systems that are dependent on regulatory gene products is proposed.
57 citations
TL;DR: The regulatory properties of the NAD-dependent malic enzyme from the mitochondria of Ascaris suum have been studied and it is proposed that this stimulation has physiological significance in controlling the dismutation reaction in the parasite.
43 citations
TL;DR: A simple and rapid method for the purification of NADP-dependent malic enzyme from chicken liver is described, which provides the enzyme in about 40% yield.
40 citations
TL;DR: The ultrastructure and 90 ° light-scattering capacity of adrenal cortex mitochondria have been examined under conditions which lead to an activation of malic enzyme activity in these mitochondria and the data are discussed as they relate to Ca 2+ -induced damage in mitochondria.
36 citations
TL;DR: The results suggest that in the cultured tobacco cells malate synthesis does not take place as a result of nitrate reduction only, but rather point to a more complex regulation in carbohydrate metabolism influenced by the extent of the prevailing synthesis of nitrogenous substances.
34 citations
TL;DR: It is deduced that ABA may have a direct effect on the electron transport of photosystem II and that the effect of ABA on the flow of 14C into individual photosynthetic products, which has been reported earlier, comes mainly from variations in stomatal behaviour.
01 Dec 1976
TL;DR: The enzymatic indices did not indicate that meal-feeding induced hyperlipogenesis can be produced in swine, and the genetic phenotype of swine is the preponderant factor regulating lipogenic enzyme activities compared to dietary manipulations.
Abstract: The effects of genetic phenotype (lean or obese), age, feeding frequency (ad-libitum or meal-fed) and dietary energy source (starch or lard) on selected enzymatic indices of lipogenesis in swine adipose tissue were investigated. The obese line maintained greater specific activities for citrate cleavage enzyme, glucose-6-phosphate dehydrogenase, 6 phosphogluconate dehydrogenase and malic enzyme compared to the lean line regardless of dietary factors. Dietary lard depressed lipogenic enzyme activity, except that of 6-phosphogluconate dehydrogenase, of adipose tissue homogenates in a similar manner in both genetic phenotypes. The enzymatic indices did not indicate that meal-feeding induced hyperlipogenesis can be produced in swine. The genetic phenotype of swine is the preponderant factor regulating lipogenic enzyme activities compared to dietary manipulations.
TL;DR: It is suggested that the NAD-linked "malic" enzyme functions in the proline-oxidation pathway predominant in tse-tse fly flight muscle.
Abstract: 1. A high activity of NAD-linked "malic" enzyme was found in homogenates of flight muscle of different species of tse-tse fly (Glossina). The activity was the same as, or higher than, that of malate dehydrogenase and more than 20-fold that of NADP-linked "malic" enzyme. A similar enzyme was found in the flight muscle of all other insects investigated, but at much lower activities. 2. ACa2+-stimulated oxaloacetate decarboxylase activity was present in all insect flight-muscle preparations investigated, in constant proportion to the NAD-linked "malic" enzyme. 3. A partial purification of the NAD-linked "malic" enzyme from Glossina was effected by DEAE-cellulose chromatography, which separated the enzyme from malate dehydrogenase and NADP-linked "malic" enzyme, but not from oxaloacetate decarboxylase. 4. The intracellular localization of the NAD-linked "malic" enzyme was predominantly mitochondrial; latency studies suggested a localization in the mitochondrial matrix space. 5. Studies on the partially purified enzyme demonstrated that it had a pH optimum between 7.6 and 7.9. It required Mg2+ or Mn2+ for activity; Ca2+ was not effective. The maximum rate was the same with either cation, but the concentration of Mn2+ required was 100 times less than that of Mg2+. Acitivity with NADP was only 1-3% of that with NAD, unless very high (greater than 10mM) concentrations of Mn2+ were present. 6. It is suggested that the NAD-linked "malic" enzyme functions in the proline-oxidation pathway predominant in tse-tse fly flight muscle.
TL;DR: The role of dietary unsaturated fat in the control of hepatic glucose-6-phosphate dehydrogenase (G6PD) and malic enzyme (ME) was studied and it is suggested that the dietary control of these enzymes involves one or more specific polyunsaturated fatty acids.
Abstract: The role of dietary unsaturated fat in the control of hepatic glucose-6-phosphate dehydrogenase (G6PD) (EC 1.1.1.49) and malic enzyme (ME) (EC 1.1.1.40) was studied in rats subjected to one or two cycles of starvation-refeeding. Rats starved and refed a control (5% corn oil) diet showed a threefold increase in G6PD activity and a twofold increase in ME activity compared to ad libitum-fed rats. After a second cycle of starvation-refeeding G6PD and ME activities showed fourfold and threefold increases, respectively, as compared to ad libitum-fed rats. Feeding rats diets containing 8% linoleic acid (as triglycerides) prevented the increase in G6PD and ME activities upon starvation-refeeding, diets with oleic, palmitic, and stearic acis when fed did not prevent this increase. Feeding rats various combinations of linoleic, linolenic and oleic acids following starvation prevented the additional increase in G6PD and ME activities after a second starvation-refeeding cycle; however, linoleic acid fed alone during the first refeeding prevented the additional increase in ME activity but not in G6PD activity. It is suggested that the dietary control of these enzymes involves one or more specific polyunsaturated fatty acids.
TL;DR: Mitochondria isolated from Jerusalem artichoke tubers oxidized endogenous NADH by both a piericidin A-sensitive and -resistant dehydrogenase if the level of oxaloacetate was kept low, and Phenylsuccinate inhibited the reduction of exogenous NAD+.
Abstract: Mitochondria isolated from Jerusalem artichoke tubers oxidized endogenous NADH by both a piericidin A-sensitive and -resistant dehydrogenase if the level of oxaloacetate was kept low. In washed mitochondria the addition of NAD+ stimulated respiration in the presence of a variety of NAD+-linked substrates. In mitochondria purified through a sucrose density gradient exogenous NAD4" caused a substantial stimulation of respiration only in the presence of malate. The apparent Km for malate was 20 ml in the absence of NAD4 and 2 mM in the presence of exogenous NAD4. The products of malate oxidation were altered by the addition of exogenous NAD4. Oxaloacetate and pyruvate were produced in equal amounts in the absence of added NAD4, but in the presence of exogenous NAD4 more pyruvate was formed. The rapid oxidation of malate in the absence of added NAD4" required phosphate while the NAD4-stimulated component was not affected by the absence of phosphate. Phenylsuccinate inhibited the reduction of exogenous NAD+ by malate ; this compound was found to inhibit isolated malate dehydrogenase and malic enzyme. Several lines of evidence suggest that electron flux through one of the NADH dehydrogenase systems may directly affect the flow through the other dehydrogenases.
TL;DR: The results indicate that the failure of citric acid cycle mutants to sporulate can be adequately explained by lack of energy and lack of glutamate.
Abstract: L-Malate repressed sporulation in the wild-type strain of Bacillus subtilis. When 75 mM L-malate was added to the growth medium at the time of inoculation, the appearance of heat-resistant spores was delayed 6 to 8 h. The synthesis of extracellular serine protease, alkaline phosphatase, glucose dehydrogenase, and dipicolinic acid was similarly delayed. Sporulation was not repressed when malate was added to the culture at t4 or later. A mutant was selected for ability to sporulate in the presence of malate. This strain could also sporulate in the presence of glucose. The malate-resistant mutant grew poorly with malate as sole carbon source, although it possessed an intact citric acid cycle, and it showed increased levels of malic enzyme. This indicates a defect in the metabolism of malate in the mutant. A mutant lacking malate dehydrogenase activity was also able to sporulate in the presence of malate. A model for the regulation of sporulation by malate is presented and discussed. Citric acid cycle intermediates other than malate did not affect sporulation. In contrast to previous results, sporulation of certain citric acid cycle mutants could be greatly increased or completely restored by the addition of intermediates after the enzymatic block. The results indicate that the failure of citric acid cycle mutants to sporulate can be adequately explained by lack of energy and lack of glutamate.
TL;DR: There were significant correlations between plasma insulin level and body weight and between plasma glucose level and the activities of malic enzyme and citrate cleavage enzyme in Avy/a mice.
Abstract: The development of obesity, hyperinsulinemia and six hepatic lipogenic enzymes in Avy/a mice were compared to that in a/a mice. Correlation between body weight, liver weight, plasma insulin concentration and activities of hepatic enzymes was analyzed. In the Avy/a mice, body weight, liver weight and plasma insulin level increased steadily as the mice aged. In the a/a mice, the change of these three parameters was much slower. Plasma insulin concentration in a/a mice did not increase until eight months of age. Compared with a/a mice, Avy/a mice had higher 6-phosphogluconate dehydrogenase and fatty acid synthetase activities at two months of age; lower citrate cleavage enzyme, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities at three months of age; lower citrate cleavage enzyme and glucose-6-phosphate dehydrogenase and higher acetyl CoA carboxylase activities at five months of age; and higher malic enzyme, citrate cleavage enzyme and 6-phosphogluconate dehydrogenase activities at eight months of age. There were significant correlations between plasma insulin level and body weight and between plasma insulin level and the activities of malic enzyme and citrate cleavage enzyme in Avy/a mice. The correlation between body weight and malic enzyme and citrate cleavage enzyme activities disappeared after the analysis was adjusted for plasma insulin level.
TL;DR: The malate-lactate fermentation is a useful procedure to prepare chiral methyl groups on a preparative scale starting from (2S, 3R) [3-H]malate.
Abstract: During the transformation of (2S, 3R) [3-3H]malate to (S) lactate no tritium exchange takes place. The stereochemical course of the decarboxylation studied with (2S, 3R) [3-2H]-malate in 3HOH/H2O and (2S, 3R) [3-3H]malate in 2H2O occurs with retention and is therefore the same as that determined by other authors for malic enzyme from vertebrates and from Escherichia coli. The malate-lactate fermentation is a useful procedure to prepare chiral methyl groups on a preparative scale starting from (2S, 3R) [3-H]malate.
TL;DR: The initial hyperlipogenesis observed in the meal-fed rat appears to be due to changes in substrate uptake by the adipose tissue and/or to alterations in enzyme activation in the adipOSE tissue rather than toChanges in the quantity of enzyme present in the tissue.
Abstract: This study was undertaken to establish the time sequence of lipogenic changes in adipose tissue of rats when converted from ad libitum feeding to meal-eating. Rats were fed a high carbohydrate diet 2 hours/day for 0 to 10 days (meal-eating). The high speed supernatant fraction from homogenized epididymal fat pads was assayed for citrate cleavage enzyme, acetyl CoA carboxylase, fatty acid synthetase and malic enzyme activities. The effects of meal-feeding on in vitro and in vivo rates of fatty acid synthesis in adipose tissue as well as the amounts of glycogen deposited in the adipose tissue were measured. During the first 10 days of meal-feeding, the lipogenic enzyme activities were actually decreased or unchanged in the meal-fed rats but during this time the in vitro and in vivo rates of fatty acid synthesis were progressively increased in the meal-fed rats. Glycogen levels in the adipose tissue of meal-fed rats were greater than the levels in the nibblers. The initial hyperlipogenesis observed in the meal-fed rat appears to be due to changes in substrate uptake by the adipose tissue and/or to alterations in enzyme activation in the adipose tissue rather than to changes in the quantity of enzyme present in the tissue.
TL;DR: A kinetic analysis indicates that inhibition is not due to chelation of Mg 2+ and suggests that oxalate binds tightly to malic enzyme after NADPH has been bound.
TL;DR: The NADP-linked malic enzyme from Halobacterium cutirubrum is strongly inhibited by acetyl-CoA and NADH, and rather weakly inhibited by oxaloacetate and glyoxylate, in the presence of very high KCl concentrations (3,M), considered physiological for the extremely halophilic bacteria.
Abstract: The NADP-linked malic enzyme from Halobacterium cutirubrum is strongly inhibited by acetyl-CoA and NADH, and rather weakly inhibited by oxaloacetate and glyoxylate, in the presence of very high KCl concentrations (3 M), considered physiological for the extremely halophilic bacteria.
TL;DR: Malic enzyme was purified from cytosol of diapausing silkworm eggs by ammonium sulphate fractionation, ion exchange chromatography on DEAE- and phosphocellulose, and calcium phosphate gel negative absorption and has an optimum pH at 8.5 and requires Mn or Mg ions for its maximum activity.
Abstract: 1. 1. Malic enzyme (malate dehydrogenase (decarboxylating) E.C. 1.1.1.40) was purified from cytosol of diapausing silkworm eggs by ammonium sulphate fractionation, ion exchange chromatography on DEAE- and phosphocellulose, and calcium phosphate gel negative absorption. 2. 2. The enzyme has an optimum pH at 8.5 and requires Mn or Mg ions for its maximum activity. 3. 3. Pyruvate is the main end product of the reaction. 4. 4. The Km for l -malate and NADP was determined to be 253 μM and 3.3 μM respectively. 5. 5. The enzyme has a mol. wt of 61,000 as determined by gel filtration.
TL;DR: The enzyme responses wereindependent of any direct effect of the diets on insulin secretion and, as might be inferred from the constant levels of liver glycogen, independent of any effect on other hormones involved in the coordination of various phases of lipid metabolism and in its integration with carbohydrate metabolism.
Abstract: On the basis of previous results which indicate that a gluten diet represses hexose monophosphate shunt dehydrogenases (HMPD) in the rat liver, the activities of glucose-6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), citrate cleavage enzyme (CCE) and malic enzyme (ME), as well as plasma insulin levels, were examined in the liver and epididymal fat pad of male rats fed diets contain ing as their nitrogenous component, either casein, gluten, or gluten supple mented with Lys and Thr after protein deprivation. The gluten diet re pressed the activities of HMPD, CCE and ME. The intensity and the nature of the repression was different in liver and in adipose tissue. In the liver the repression of HMPD was greater than that of CCE and ME and in no case was the enzyme repression prevented by addition of Lys and Thr to the gluten diet. In the adipose tissue the repression of CCE and ME was greater than that of HMPD and in all cases the repression was pre vented by addition of Lys and Thr. The enzyme responses were inde pendent of any direct effect of the diets on insulin secretion and, as might be inferred from the constant levels of liver glycogen, independent of any effect on other hormones involved in the coordination of various phases of lipid metabolism and in its integration with carbohydrate metabolism. These results are consistent with the view that in the liver the levels of lipogenic enzymes are controlled by different regulatory mechanisms than in the adipose tissue. J. Nutr. 106: 335-341, 1976. INDEXING
TL;DR: Findings indicated that, at the beginning of luteolysis and fetal resorption, the activities of steroidogenic enzymes decreased and 20alpha-HSD was not yet activated.
TL;DR: Diurnal variations were observed in the activities of phosphoenolpyruvate carboxylase, «malic» enzyme and acidity in Cuscata reflexa filaments.
TL;DR: The results indicate that enhanced flux of metabolites into lipids reflects a virus-induced alteration in embryonic development: the enzyme patterns of infected embryos are more characteristic of older embryos or even newly hatched chicks.
01 Jan 1976
TL;DR: The characteristics of02 uptake bysweet potato mitochondria in response tomalate are detailed, and showsthatthe saturation isotherm formalate isbimodal, withanintermediary plateau, and evidence that this response isindicative of dualpathways ofmalate metabolism inthese mitochondria.
Abstract: Overarange ofconcentrations fromless than0.1mMtomorethan70 mM,sweet potato rootmitochondria display abimodal substrate saturation isotherm formalate. Thehighaffinity portion oftheisotherm hasan apparent Km formalate of0.85mm andfits arectangular hyperbolic function. Thelowaffinity portion oftheisotherm issigmoid incharacter andgives anapparent S0.5 of40.6mm andaHill numberof3.7. Extracts ofsweet potato mitochondria contain bothmalate dehydrogenase andNAD malic enzyme. Themalate dehydrogenase, assayed in theforward direction atpH7.2, showstypical Michaelis-Menten kinetics witha Km formalate of0.38mm.TheNAD malic enzymeshows pronounced sigmoidicity inresponse tomalate with aHill numberof3.5 andanS05of41.6mM. On thebasis ofthenormalkinetics, theKm,andthefactthat oxaloacetate production frommalate bymitochondria appears most active atlowmalate concentrations, thehighaffinity portion ofthe malate isotherm with mitochondria isattributed tomalate dehydrogenase. Thelowaffinity portion ofthemalate isotherm with mitochondria is thought, onthebasis ofthesimilarity ofSO.5 values, theHill numbers, andthegreater production ofpyruvate frommalate athighmalate concentrations, torepresent theactivity oftheNAD malic enzyme. Theresponseofplant mitochondria tomalate isoften variable anderratic (6,10,12,13,15).Saturation withthesubstrate is difficult toachieve, coupling withphosphorylation issometimes lessthanwithothertricarboxylic acidcyclesubstrates using NAD asacofactor (16)andtheresponsetoexogenously added cofactors suchasNAD may beatvariance withthatofother substrates (3,6,15).Inpart,these unexpected responsesmay arise fromthecharacteristics oftheenzyme,malate dehydrogenase,usually assumed toberesponsible fortheoxidation of malate inthetricarboxylic acidcycle. Malatedehydrogenase is strongly inhibited byitsproduct, oxaloacetate, atpH values in therangelikely tobefoundinthemitochondria (10,17,18), andissubject toallosteric regulation bya numberofeffectors (1). We haveobserved inmitochondria froma variety ofplant tissues, including sweetpotato, beetroots,cauliflower florets, andArumspadix, afailure of02 uptake ratestobesaturated by levels ofmalategreatly inexcessoftheconcentrations which wouldbeexpected toelicit no further responseon thebasis of theobserved Km formalate ofmalatedehydrogenase inmitochondrial extracts. Inaddition, itisfrequently difficult toobtain smooth curvesinthe02 uptake responseofplant mitochondria tomalate, andwheresufficient numbersofcareful determinations are made,themalate responsecurve appearstobeinflected. Similar results havebeenobtained byothers (3,13). Thisreportdetails thecharacteristics of02 uptake bysweet potato mitochondria inresponse tomalate, andshowsthatthe saturation isotherm formalate isbimodal, withanintermediary plateau, andprovides evidence that this response isindicative of dualpathways ofmalate metabolism inthese mitochondria, one through malatedehydrogenase tooxaloacetate, theother through NAD malic enzymetopyruvate.