Low Malate Concentrations Research Articles

Long-Chain and Medium-Chain Fatty Acids in Energy Metabolism of Murine Kidney Mitochondria

Scientists have long established that fatty acids are the primary substrates for kidney mitochondria. However, to date we still do not know how long-chain and middle-chain fatty acids are oxidized at the mitochondrial level. Our previous research has shown that mitochondria from the heart, brain, and kidney oxidize palmitoylcarnitine at a high rate only in the presence of succinate, glutamate, or pyruvate. In this paper, we report properties of the isolated kidney mitochondria and how malate and succinate affect the oxidation of C16 and C8 acylcarnitines. The isolated kidney mitochondria contain very few endogenous substrates and require malate to oxidize pyruvate, glutamate, and C16 or C8 acylcarnitines. We discovered that with 10 µM of C16 or C8 acylcarnitines, low concentrations of malate (0.2 mM) or succinate (0.5 mM) enhance the States 4 and 3 respiratory rates several times. The highest respiration rates were observed with C16 or C8 acylcarnitines and 5 mM succinate mixtures. Results show that kidney mitochondria, unlike the heart and brain mitochondria, lack the intrinsic inhibition of succinate dehydrogenase. Additionally, results show that the oxidation of fatty acid by the small respirasome's supercomplex generates a high level of CoQH2, and this makes SDH in the presence of succinate reverse the flow of electrons from CoQH2 to reduce fumarate to succinate. Finally, we report evidence that succinate dehydrogenase is a key mitochondrial enzyme that allows fast oxidation of fatty acids and turns the TCA cycle function from the catabolic to the anabolic and anaplerotic metabolic pathways.

Concentrations of Nitrate, Organic Acids, Free Amino Acids, Cations and Sugars in Komatsuna (Brassica campestris var. perviridis) Grown with Carbonate, Sulfate and Chloride Application

This study compared the concentrations of components such as nitrate, organic acids, free amino acids, cations and sugars in komatsuna (Brassica campestris var. perviridis) grown with carbonate, sulfate and chloride application (CO3-TK, SO4-TK and Cl-TK, respectively). The komatsuna was cultivated in 1/2000-a Wagner pots (6 hills per pot) filled with light-colored Andosol in a glasshouse for 37 days at soil water potential (SWP) right before harvesting of −6.2 and −62 kPa. And 26.5 mmolc of carbonate, sulfate or chloride in the form of potassium salts was applied to each pot. Chloride application to the komatsuna induced relatively high concentrations of potassium, calcium and magnesium ions, and the low concentrations of malate, glucose and fructose on a dry weight basis (DWB). Carbonate application induced relatively high concentrations of malate and low concentrations of nitrate. Sulfate was almost between chloride and carbonate. Concentration variation was not substantial in free amino acids. Those tendencies were almost the same in both SWPs. Most of the variations in component concentrations were attributed to the regulation of ionic and osmotic balance to respond to chloride, nitrate and sulfate absorption, as judged from quantitative relationships among the components and water in the komatsuna. It seems that the absorption of nitrate is influenced by the pH of the soil. There were clear differences in glucose, fructose and malate concentrations among CO3-TK, SO4-TK and Cl-TK on a fresh weight basis just as on a DWB.

Aluminum speciation studies in biological fluids. Part 7. A quantitative investigation of aluminum(III)-malate complex equilibria and their potential implications for aluminum metabolism and toxicity.

As a nonessential element, aluminum may be toxic at both environmental and therapeutic levels, depending on ligand interactions. Dietary acids that normally occur in fruits and vegetables and commonly serve as taste enhancers are good ligands of the Al(3+) ion. Malic acid is one of these and also one of the most predominant in food and beverages. The present paper reports an examination of its potential influence on aluminum bioavailability through speciation calculations based on Al(III)-malate complex formation constants especially determined for physiological conditions. According to the results obtained, malate appears to be extremely effective in maintaining Al(OH)(3) soluble over the whole pH range of the small intestine under normal dietary conditions. In addition, two neutral Al(III)--malate complexes are formed whose percentages are maximum from very low malate levels. When aluminum is administered therapeutically as its trihydroxide, the amount of metal neutralized by malate peaks as its solubility pH range regresses to its original limits in the absence of malate. The enhancing effect of malate towards aluminum absorption is therefore virtually independent of the aluminum level in the gastrointestinal tract. The presence of phosphate in the gastrointestinal juice is expected to limit the potential influence of malate on aluminum absorption. Under normal dietary conditions, phosphate effectively reduces the fraction of aluminum neutralized by malate but without nullifying it. Aluminum phosphate is predicted to precipitate when aluminum levels are raised as with the administration of aluminum hydroxide, but a significant amount of neutral aluminum malate still remains in solution. Even therapeutic aluminum phosphate is not totally safe in the presence of malate, even at low malate concentrations. As plasma simulations predict that no compensatory effect in favor of aluminum excretion may be expected from malate, simultaneous ingestion of malic acid with any therapeutic aluminum salt should preferably be avoided.

Physiology of pre-cut mango II. Evolution of organic acids

The effect of a 30-min osmotic dehydration (OD) treatment under vacuum and storage temperature on the organic acid content in slices prepared from Haden and Kent mangoes was evaluated. Additionally, respiration rate (RR), titratable acidity, pH and soluble solids were monitored. Greater RR was detected in osmotically dehydrated slices. Citric, ascorbic and fumaric acids were measured in greater concentrations in Haden slices, while malic acid was predominant in Kent slices. No succinic acid was found in any sample. Low malate concentrations suggest that the observed increase in CO 2 production caused by the mechanical stress may be due to malic acid decarboxylation by the malic enzyme. OD caused lesser alterations in oganic acid balance than cutting and possibly allowed an extended operation of the tricarboxylic acid cycle.

Regulation of mitochondrial and cytosolic malic enzymes from cultured rat brain astrocytes.

Malate has a number of key roles in the brain, including its function as a tricarboxylic acid (TCA) cycle intermediate, and as a participant in the malate-aspartate shuttle. In addition, malate is converted to pyruvate and CO2 via malic enzyme and may participate in metabolic trafficking between astrocytes and neurons. We have previously demonstrated that malate is metabolized in at least two compartments of TCA cycle activity in astrocytes. Since malic enzyme contributes to the overall regulation of malate metabolism, we determined the activity and kinetics of the mitochondrial and cytosolic forms of this enzyme from cultured astrocytes. Malic enzyme activity measured at 37 degrees C in the presence of 0.5 mM malate was 4.15 +/- 0.47 and 11.61 +/- 0.98 nmol/min/mg protein, in mitochondria and cytosol, respectively (mean +/- SEM, n = 18-19). Malic enzyme activity was also measured in the presence of several endogenous compounds, which have been shown to alter intracellular malate metabolism in astrocytes, to determine if these compounds affected malic enzyme activity. Lactate inhibited cytosolic malic enzyme by a noncompetitive mechanism, but had no effect on the mitochondrial enzyme. alpha-Ketoglutarate inhibited both cytosolic and mitochondrial malic enzymes by a partial noncompetitive mechanism. Citrate inhibited cytosolic malic enzyme competitively and inhibited mitochondrial malic enzyme noncompetitively at low concentrations of malate, but competitively at high concentrations of malate. Both glutamate and aspartate decreased the activity of mitochondrial malic enzyme, but also increased the affinity of the enzyme for malate. The results demonstrate that mitochondrial and cytosolic malic enzymes have different kinetic parameters and are regulated differently by endogenous compounds previously shown to alter malate metabolism in astrocytes. We propose that malic enzyme in brain has an important role in the complete oxidation of anaplerotic compounds for energy.

Different regulatory properties of the cytosolic and mitochondrial forms of malic enzyme isolated from human brain

The human brain contains a cytosolic and mitochondrial form of NADP +-dependent malic enzyme. To investigate their possible metabolic roles we compared the regulatory properties of these two iso-enzymes. The mitochondrial malic enzyme exhibited a sigmoid substrate saturation curve at low malate concentration which was shifted to the right at both higher pH values and in the presence of low concentration of Mn 2+ or Mg 2+. Succinate or fumarate increased the activity of the mitochondrial malic enzyme at low malate concentration. Both activators shifted the plot of reaction velocity versus malate concentration to the left, and removed sigmoidicity, but the maximum velocity was unaffected. The activation was associated with a decrease in Hill coefficient from 2.3 to 1.1. The human brain cytosolic malic enzyme displayed a hyperbolic substrate saturation kinetics and no sigmoidicity was detected even at high pH and low malate concentrations. Succinate or fumarate exerted no effect on the enzyme activity. Excess of malate inhibited the oxidative decarboxylation catalysed by cytosolic enzyme at pH 7.0 and below. In contrast, decarboxylation catalysed by mitochondrial malic enzyme, was unaffected by the substrate. These results suggest that under in vivo conditions, cytosolic malic enzyme catalyses both oxidative decarboxylation of malate and reductive carboxylation of pyruvate, whereas the role of mitochondrial enzyme is limited to decarboxylation of malate. One may speculate that in vivo the reaction catalysed by cytosolic malic enzyme supplies dicarboxylic acids (anaplerotic function) for the formation of neurotransmitters, while the mitochondrial enzyme regulates the flux rate via Krebs cycle by disposition of the tricarboxylic acid cycle intermediates (cataplerotic function).

The metabolism of malate by cultured rat brain astrocytes

Since malate is known to play an important role in a variety of functions in the brain including energy metabolism, the transfer of reducing equivalents and possibly metabolic trafficking between different cell types; a series of biochemical determinations were initiated to evaluate the rate of 14CO2 production from L-[U-14C]malate in primary cultures of rat brain astrocytes. The 14CO2 production from labeled malate was almost totally suppressed by the metabolic inhibitors rotenone and antimycin A suggesting that most of malate metabolism was coupled to the electron transport system. A double reciprocal plot of the 14CO2 production from the metabolism of labeled malate revealed biphasic kinetics with two apparent Km and Vmax values suggesting the presence of more than one mechanism of malate metabolism in these cells. Subsequent experiments were carried out using 0.01 mM and 0.5 mM malate to determine whether the addition of effectors would differentially alter the metabolism of high and low concentrations of malate. Effectors studied included compounds which could be endogenous regulators of malate metabolism and metabolic inhibitors which would provide information regarding the mechanisms regulating malate metabolism. Both lactate and aspartate decreased 14CO2 production from 0.01 mM and 0.5 mM malate equally. However, a number of effectors were identified which selectively altered the metabolism of 0.01 mM malate including aminooxyacetate, furosemide, N-acetylaspartate, oxaloacetate, pyruvate and glucose, but had little or no effect on the metabolism of 0.5 mM malate. In addition, alpha-ketoglutarate and succinate decreased 14CO2 production from 0.01 mM malate much more than from 0.5 mM malate. In contrast, a number of effectors altered the metabolism of 0.5 mM malate more than 0.01 mM. These included methionine sulfoximine, glutamate, malonate, alpha-cyano-4-hydroxycinnamate and ouabain. Both the biphasic kinetics and the differential action of many of the effectors on the 14CO2 production from 0.01 mM and 0.5 mM malate provide evidence for the presence of more than one pool of malate metabolism in cultured rat brain astrocytes.

Kinetic mechanism in the direction of oxidative decarboxylation for NAD-malic enzyme from Ascaris suum.

Measurement of the initial rate of the malic enzyme reaction varying the concentration of NAD at several different fixed levels of Mg2+ (0.25-1.0 mM) and a single malate concentration gave a pattern which intersects to the left of the ordinate. Repetition of this initial velocity pattern at several additional malate concentrations and treatment in terms of a terreactant mechanism suggests an ordered mechanism in which NAD adds prior to Mg2+ which must add prior to malate. On the other hand, when a broader concentration range of Mg2+ (0.25-50 mM) is used, data are consistent with a random mechanism in which Mg2+ must add prior to malate. By use of product inhibition studies, pyruvate is competitive vs. malate and noncompetitive vs. NAD, while NADH is competitive vs. NAD and noncompetitive vs. malate. These results are consistent with the random addition of substrates and further suggest rapid equilibrium random release of products. Tartronate, a dead-end analogue of malate, is competitive vs. malate and noncompetitive vs. NAD. Thio-NAD is a slow substrate which is used at 2.4% the maximum rate of NAD. When used as a dead-end analogue of NAD, thio-NAD is competitive vs. NAD and gives a complex inhibition pattern vs. malate in which competitive inhibition is apparent at low concentrations of malate (less than 12.5 mM), and this changes to uncompetitive inhibition at high concentrations of malate (greater than 12.5 mM). These data are consistent with a steady-state random mechanism in the direction of oxidative decarboxylation in which Mg2+ adds in rapid equilibrium prior to malate.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamine, glutamate, and other possible regulators of alpha-ketoglutarate and malate uptake by synaptic terminals.

The uptake of alpha-ketoglutarate and malate by rat brain synaptosomal preparations was found to be affected by a variety of substances at physiologically relevant concentrations. Glutamine altered the uptake of alpha-ketoglutarate by causing an apparent reduction in the substrate-carrier affinity and an increase in Vmax. In contrast, glutamine did not appear to affect the Vmax of malate uptake, but it did increase markedly the uptake velocity at low concentrations of malate. L-Glutamate and L-aspartate were comparatively strong inhibitors of alpha-ketoglutarate and malate uptake. N-Acetylaspartate was a weak inhibitor of alpha-ketoglutarate uptake, a finding that contrasts with our previous observation that this compound potently inhibited alpha-ketoglutarate uptake by synaptosomes obtained from the cerebellum of 8- to 14-day-old mice. Ca2+ exhibited a variable effect but usually enhanced the uptake of alpha-ketoglutarate. The addition of small amounts of postmicrosomal supernatant to the incubation medium enhanced the uptake of alpha-ketoglutarate by low-density synaptosomes. By comparison, the uptake of glutamate, glutamine, gamma-aminobutyric acid, and several other amino acids was not affected. The enhancement of alpha-ketoglutarate uptake by the supernatant was due to a heat labile substance that was retained by dialysis tubing (MW cutoff = 8,000) and Amicon filter cones (CF 25), and was precipitated by ammonium sulfate at 60% saturation. In experiments in which the metabolic conversion of [U-14C] alpha-ketoglutarate to glutamate, aspartate, glutamine, and gamma-aminobutyric acid was determined, the presence of glutamine and glutamate in the incubation medium did not affect the pattern of labelling appreciably.

Changes in the electron transport chain of pea leaf mitochondria metabolizing malate

Pea leaf mitochondria showed complex kinetics for malate metabolism. O 2 uptake increased as malate concentration increased from 0 to 10 m m, reached a plateau between 10 and 20 m m malate, and then increased again up to 40 m m malate. Analysis of the products of malate oxidation by high-performance liquid chromatography revealed that the first phase of O 2 uptake coincided with the synthesis of both pyruvate and oxalacetate (OAA) while the second phase of O 2 uptake at higher malate levels usually occurred with a large increase in OAA formation. The biphasic response in O 2 uptake and the changing ratios of pyruvate and OAA synthesis did not appear to be the direct result of the differing K m values of malate dehydrogenase and malic enzyme. Rather, they resulted from thermodynamic properties of these two malate oxidases and the kinetics of the two NADH dehydrogenases found in plant mitochondria. At low malate concentrations the rotenone-sensitive NADH dehydrogenase was active and could accept electrons from both malate oxidases. This NADH dehydrogenase became saturated at about 10 m m malate. At higher malate concentrations the rotenone-insensitive NADH dehydrogenase was increasingly important and its increased electron transport capacity was best exploited by malate dehydrogenase. At the higher malate concentrations an increasing portion of the electrons from malate reduce O 2 through the alternative oxidase. Although this coincided with the second phase of malate-dependent O 2 uptake it was not required for this phase to be seen.

In vitro production of propionate by mantle mitochondria of the sea mussel Mytilus edulis L.: Overall mechanism

1. 1. In this study it is demonstrated that mantle mitochondria of Mytilus edulis L. possess the enzyme system to convert succinate into propionate. 2. 2. The in vitro propionate synthesis is optimal at a succinate concentration of about 16 mM at pH 6.7. ADP, inorganic phosphate and Mg 2+ are required while relative low concentrations of malate markedly enhance the formation of propionate. 3. 3. It is suggested that malate provides succinyl-CoA through 2-oxoglutarate and thus sparks the synthesis of propionate.

Slow Transients in the Activity of the NAD Malic Enzyme from Crassula

The NAD malic enzyme from Crassula argentea shows a slow reaction transient in the form of a lag before reaching a steady-state rate in assays. This lag, which has a half-time or tau ranging from seconds to many minutes under various conditions, poses problems in the interpretation of kinetic data with this enzyme. The NAD malic enzyme from Kalanchoë daigremontiana has a similar lag.The lag is greatest in freshly prepared enzyme and diminishes with storage at -70 degrees C, but the activity of the enzyme also diminishes with storage.The lag is inversely proportional to the concentration of enzyme, both in the assay and in storage prior to assay. The lag is also inversely proportional to the concentration of malate used in the assay, which poses particular problems because the lag with low malate concentrations may be so long that activity begins to be lost before the steady-state rate is reached.Various buffer ions produce different lags, but the lag with all buffers is longer than in the absence of buffer. The effectors CoA and SO(4) (2-) in the assay substantially decrease the lag. The lag is shorter with Mn(2+) as the required divalent cation than when Mg(2+) is used.The response of enzyme activity to pH shows that the intrinsic activity is greater with magnesium than with manganese, although the rate actually attained is lower with Mg(2+) because the pK values for the response to pH are closer together when that cation is used. The enzyme has a higher optimum pH and a broader response to pH when Mn(2+) is used. The change in lag with pH follows the general pattern of activity with longer lags at intermediate pH values.Preincubation of the enzyme with various reaction components and effectors reduces the lag, with NADH being the most effective. The presence of NADH in the assay is much more effective, but none of the treatments tried will completely eliminate the lag of freshly prepared enzyme.

Polarographic Study of Dicarboxylic-Acid-dependent Export of Reducing Equivalents from Illuminated Chloroplasts

Isolated pea chloroplasts, prepared by differential centrifugation, catalyzed O(2) evolution in the light in the presence of 0.03 to 3 millimolar malate, 0.12 to 1.2 millimolar NAD, 4 millimolar pyruvate and exogenous NAD-malate dehydrogenase and lactate dehydrogenase. The reaction, which did not occur in the absence of any one of these factors, was accompanied by the consumption of pyruvate; the ratio of O(2) evolved to pyruvate consumed was <0.5. When 0.1 millimolar [(14)C]malate was supplied most of the (14)C label was recovered as malate. At low concentrations of malate (<0.1 millimolar), the ratio of O(2) evolved to malate supplied was greater than 0.5.Chloroplasts catalyzed oxaloacetate-dependent O(2) evolution in approximate agreement with the theoretical stoichiometry for the light-coupled reduction of oxaloacetate to malate. Subsequent addition of NAD, pyruvate, NAD-malate dehydrogenase, and lactate dehydrogenase caused immediate resumption of O(2) evolution with the concomitant reduction of pyruvate to lactate externally to the chloroplasts. Resumption of O(2) evolution did not occur in the absence of oxaloacetate. The results are consistent with a mechanism in which oxaloacetate/malate cycles continuously between the chloroplasts and the external solution and serves as a carrier for the transfer of light-generated reducing equivalents for pyruvate reduction outside the chloroplast.

Malate Dehydrogenase and NAD Malic Enzyme in the Oxidation of Malate by Sweet Potato Mitochondria

Over a range of concentrations from less than 0.1 mm to more than 70 mm, sweet potato root mitochondria display a bimodal substrate saturation isotherm for malate. The high affinity portion of the isotherm has an apparent Km for malate of 0.85 mm and fits a rectangular hyperbolic function. The low affinity portion of the isotherm is sigmoid in character and gives an apparent S(0.5) of 40.6 mm and a Hill number of 3.7.Extracts of sweet potato mitochondria contain both malate dehydrogenase and NAD malic enzyme. The malate dehydrogenase, assayed in the forward direction at pH 7.2, shows typical Michaelis-Menten kinetics with a Km for malate of 0.38 mm. The NAD malic enzyme shows pronounced sigmoidicity in response to malate with a Hill number of 3.5 and an S(0.5) of 41.6 mm.On the basis of the normal kinetics, the Km, and the fact that oxaloacetate production from malate by mitochondria appears most active at low malate concentrations, the high affinity portion of the malate isotherm with mitochondria is attributed to malate dehydrogenase. The low affinity portion of the malate isotherm with mitochondria is thought, on the basis of the similarity of S(0.5) values, the Hill numbers, and the greater production of pyruvate from malate at high malate concentrations, to represent the activity of the NAD malic enzyme.

Effects of High Concentrations of KC1 and NaCl on Responses of Malate Dehydrogenase (Decarboxylating) to Malate and Various Inhibitors

The effects of KC1 on catalytic and allosteric properties of malate dehydrogenase (decarboxylating) were studied. Chloride salts (50 mM and higher) strongly inhibited enzyme activity at low malate concentrations. At high malate (4 mM) , on the other hand, the degree of inhibition induced by chloride was very small. The s0.5 value (i.e. the malate concentration required for half maximum velocity) was about 0.4 mM in the absence of KC1 and increased to 0.75 and 1.5 mM at 50 and 100 mM KC1 respectively. High chloride concentrations also removed a small degree of substrate inhibition, which in the absence of KC1 occurred at 8 mM malate. At low malate concentrations (&lt; 0 . 5 mM) 50 mM KC1 increased the Hill number from 1.3 to 1.9. Thus chloride treatment revealed a strong degree of cooperativity for the enzyme. This potential for homotropic effects was much less realized in MES buffer (potassium salt), presumably because affinity of malate for individual active sites was already very high. These effects of KC1 were readily reversible and the enzyme showed no appreciable change in molecular weight in the presence of 200 mM KCl. At malate concentrations between 1 and 12 mM, inhibitions of malate dehydrogenase (decarboxylating) activity induced by oxaloacetate, D-malate, and phosphoglycerate were reduced by KCl. At low malate concentrations, on the other hand, the inhibitory effect induced by oxaloacetate changed to a strong stimulatory effect in the presence of KCl. The inhibitory effect due to oxaloacetate was greatly diminished in malate dehydrogenase (decarboxylating) which was eluted from a DE52 cellulose column, but the inhibitory effect due to KC1 was retained. Elution from DE52 cellulose also reduced the Hill number to 1 and increased the s0.5 value. The above results suggest that KC1 reduced the affinity of both substrate and some allosteric inhibitors of malate dehydrogenase (decarboxylating).

The transport of inorganic phosphate by the mitochondrial dicarboxylate carrier.

1. N-Ethylmaleimide inhibited the influx and efflux of P(i) in rat liver mitochondria. 2. The efflux was stimulated by either succinate or malate in the presence of N-ethylmaleimide, and this stimulation was reversed by 2-n-butylmalonate. 2-Oxoglutarate and citrate, even in the presence of low concentrations of malate, were relatively ineffective in stimulating efflux of P(i) under these conditions, as was glutamate. 3. By using radioactively labelled P(i) and dicarboxylate ions an exchange was demonstrated, the stoicheiometry of which was 1.3+/-0.5 dicarboxylate ions:1 P(i) (n=10). 4. An exchange between unlabelled and labelled P(i) in the presence of N-ethylmaleimide was found which was sensitive to 2-n-butylmalonate. 5. It is concluded that the mitochondrial dicarboxylate carrier can transport phosphate by an exchange diffusion with certain penetrant dicarboxylic acids or with phosphate itself. The exchange mechanism is sensitive to 2-n-butylmalonate but is unaffected by N-ethylmaleimide; the action of mersalyl in this context is commented on.

Allosteric characteristics of bovine heart mitochondrial malic enzyme

The mitochondrial isozyme of malic enzyme from bovine heart shows allosteric properties at low concentrations of malate and this characteristic can be modified by succinate, which does not affect the maximum velocity of the reaction. The cytoplasmic isozyme from the same tissue does not show any allosteric properties.

ROOT GROWTH AND DARK FIXATION OF CARBON DIOXIDE IN CALCICOLES AND CALCIFUGES

SummaryThe inhibition of root growth by bicarbonate ions has been further investigated by an examination of the process of dark fixation of carbon dioxide by Arrhenatherum elatius and Deschampsia flexuosa. Excised roots incorporated [14C]bicarbonate mostly into malate in 4 hours. Intact plants grown on solutions containing 10 m‐equiv./1 bicarbonate for 24 hours showed large increases in the total acid content of the roots. Malate was increased in both species and citrate also in Arrhenatherum elatius. The increases in total acidity were similar and could be explained solely by the dark fixation of bicarbonate. Seedlings grown on solutions of sodium hydrogen malate showed similar inhibitions to those observed on sodium bicarbonate solutions. Root growth of Deschampsia flexuosa was inhibited throughout a range of malate concentrations (1–20 m‐equiv./l) whereas Arrhenatherum elatius was stimulated at low malate concentrations and only slightly inhibited at 20 m‐equiv/1. The inhibiting action of bicarbonate on the root growth of Deschampsia flexuosa is associated with the increase in malate in the roots by dark fixation. The results are discussed in terms of the organic acid content and metabolism of calcicole and calcifuge species.