Malatic acid

A. Plisson. Sisr I Identite du malate acide d altheine avec I asparagine. Ann. Chim. et Phys., 1827, 36, 175-183. 

Colourless prisms m.p. 130 C. Manufactured by treating maleic anhydride with water. It is converted to the anhydride by heating at By prolonged heating at 150 "C or by heating with water under pressure at 200 C, it is converted to the isomeric (trans) fumaric acid. Reduced by hydrogen to succinic acid. Oxidized by alkaline solutions of potassium permanganate to mesotartaric acid. When heated with solutions of sodium hydroxide at 100 C, sodium( )-malate is formed. Used in the preparation of ( )-malic acid and in some polymer formulations. 

H02C(CH2)2C02H. Colourless prisms m.p. 182 C, b.p. 235°C. Occurs in amber, algae, lichens, sugar cane, beets and other plants, and is formed during the fermentation of sugar, tartrates, malates and other substances by a variety of yeasts, moulds and bacteria. Manufactured by the catalytic reduction of maleic acid or by heating 1,2-dicyanoethane with acids or alkalis. Forms an anhydride when heated at 235°C. Forms both acid and neutral salts and esters. Used in the manufacture of succinic anhydride and of polyesters with polyols. 

Alkyl hahdes in the presence of silver oxide react with alkyl malates to yield alkoxy derivatives of succinic acid, eg, 2-ethoxysuccinic acid, H00CCH2CH(0C2H )C00H (12,13). A synthetic approach to produce ethers of malic acid is the reaction of malic esters and sodium alkoxides which affords 2-alkoxysuccinic esters (14). 

Ca.ndy. Its low melting point and sugar inversion properties make malic acid a desirable acidulant, especially in hard candy products (44,45). Due to their insolubiUty, hard water salts can cause clouding of the finished product. However, because of the higher solubiUty of calcium malate [17482-42-7] relative to alternative acidulants, clarity of the finished product is enhanced. Additionally, in sugar confectionery products where acidulation may exceed 2.0%, malic acid can provide economic benefits. 

OC-Hydroxycarboxylic Acid Complexes. Water-soluble titanium lactate complexes can be prepared by reactions of an aqueous solution of a titanium salt, such as TiCl, titanyl sulfate, or titanyl nitrate, with calcium, strontium, or barium lactate. The insoluble metal sulfate is filtered off and the filtrate neutralized using an alkaline metal hydroxide or carbonate, ammonium hydroxide, amine, or alkanolamine (78,79). Similar solutions of titanium lactate, malate, tartrate, and citrate can be produced by hydrolyzation of titanium salts, such as TiCl, in strongly (>pH 10) alkaline water isolation of the... 

We detenuined the influence of oxy- and ketocarboxylic acids (succinate, fumarate, adipinate, a-ketoglutarate, isocitrate, tartrate, E-malate) on the luminescence intensity of the Eu-OxTc complex. These substances interact as polydentate ligands similarly to citrate with the formation of ternary complexes with Eu-OxTc. As to succinate, fumarate, adipinate and a-ketoglutarate this they cannot effectively coordinate with EiT+ and significant fluorescence enhancement was not observed. 

The mother liquors from the original cr3 Stallization and recrystallizations are treated in a similar manner and the sodium malate solutions are united and reserved for the recovery of i-malic acid (Note 7). The recovered amine amounts to 75-80 g. and contains 40-50 per cent excess /-amine. 

The purity of (/-a-phenylethylamine-/-malate is not readily determined by its melting point or specific rotation, but rather by its massive crystalline form and solubility. The acid and neutral /-base-/-acid salts are much more soluble, and usually do not crystallize at all. 

The solution containing sodium malate is neutralized with acetic acid, diluted to contain about 5 per cent of sodium... 

The procedure for preparing 6-hydroxynicotinic acid is also based on a method described by von Pechmann. 6-Hydroxynico-tinic acid has also been prepared by decarboxylation of 6-hy-droxy-2,3-pyridinedicarboxylic acid by heating 6-hydra-zinonicotinic acid or its hydrazide with hydrochloric acid by the action of carbon dioxide on the sodium salt of a-pyridone at 180-200 and 20 atmospheres by heating the nitrile of 6-chlo-ronicotinic acid with alcoholic sodium hydroxide or hydrochloric acid from 6-aminonicotinic acid and by the prolonged action of concentrated ammonium hydroxide on methyl cou-malate. ... 

In the resolution of 1-phenylethylamine using (-)-malic acid, the compound obtained by recrystallization of the mixture of diastereomeric salts is (/ )-1-phenylethylammonium (S)-malate. The other component of the mixture is more soluble and remains in solution. What is the configuration of the more soluble salt ... 

In 1932 Krebs was studying the rates of oxidation of small organic acids by kidney and liver tissue. Only a few substances were active in these experiments —notably succinate, fumarate, acetate, malate, and citrate (Figure 20.2). Later it was found that oxaloacetate could be made from pyruvate in such tissues, and that it could be further oxidized like the other dicarboxylic acids. 

In 1937 Krebs found that citrate could be formed in muscle suspensions if oxaloacetate and either pyruvate or acetate were added. He saw that he now had a cycle, not a simple pathway, and that addition of any of the intermediates could generate all of the others. The existence of a cycle, together with the entry of pyruvate into the cycle in the synthesis of citrate, provided a clear explanation for the accelerating properties of succinate, fumarate, and malate. If all these intermediates led to oxaloacetate, which combined with pyruvate from glycolysis, they could stimulate the oxidation of many substances besides themselves. (Kreb s conceptual leap to a cycle was not his first. Together with medical student Kurt Henseleit, he had already elucidated the details of the urea cycle in 1932.) The complete tricarboxylic acid (Krebs) cycle, as it is now understood, is shown in Figure 20.4. 

Finally, citrate can be exported from the mitochondria and then broken down by ATP-citrate lyase to yield oxaloacetate and acetyl-CoA, a precursor of fatty acids (Figure 20.23). Oxaloacetate produced in this reaction is rapidly reduced to malate, which can then be processed in either of two ways it may be transported into mitochondria, where it is reoxidized to oxaloacetate, or it may be oxidatively decarboxylated to pyruvate by malic enzyme, with subse-... 

FIGURE 20.23 Export of citrate from mitochondria and cytosolic breakdown produces oxaloacetate and acetyl-CoA. Oxaloacetate is recycled to malate or pyruvate, which re-enters the mitochondria. This cycle provides acetyl-CoA for fatty acid synthesis in the cytosol. 

Compartmentation of these reactions to prevent photorespiration involves the interaction of two cell types, mescrphyll cells and bundle sheath cells. The meso-phyll cells take up COg at the leaf surface, where Og is abundant, and use it to carboxylate phosphoenolpyruvate to yield OAA in a reaction catalyzed by PEP carboxylase (Figure 22.30). This four-carbon dicarboxylic acid is then either reduced to malate by an NADPH-specific malate dehydrogenase or transaminated to give aspartate in the mesophyll cells. The 4-C COg carrier (malate or aspartate) then is transported to the bundle sheath cells, where it is decarboxylated to yield COg and a 3-C product. The COg is then fixed into organic carbon by the Calvin cycle localized within the bundle sheath cells, and the 3-C product is returned to the mesophyll cells, where it is reconverted to PEP in preparation to accept another COg (Figure 22.30). Plants that use the C-4 pathway are termed C4 plants, in contrast to those plants with the conventional pathway of COg uptake (C3 plants). 

Succinyl-CoA derived from propionyl-CoA can enter the TCA cycle. Oxidation of succinate to oxaloacetate provides a substrate for glucose synthesis. Thus, although the acetate units produced in /3-oxidation cannot be utilized in glu-coneogenesis by animals, the occasional propionate produced from oxidation of odd-carbon fatty acids can be used for sugar synthesis. Alternatively, succinate introduced to the TCA cycle from odd-carbon fatty acid oxidation may be oxidized to COg. However, all of the 4-carbon intermediates in the TCA cycle are regenerated in the cycle and thus should be viewed as catalytic species. Net consumption of succinyl-CoA thus does not occur directly in the TCA cycle. Rather, the succinyl-CoA generated from /3-oxidation of odd-carbon fatty acids must be converted to pyruvate and then to acetyl-CoA (which is completely oxidized in the TCA cycle). To follow this latter route, succinyl-CoA entering the TCA cycle must be first converted to malate in the usual way, and then transported from the mitochondrial matrix to the cytosol, where it is oxida-... 

The acetyl-CoA derived from amino acid degradation is normally insufficient for fatty acid biosynthesis, and the acetyl-CoA produced by pyruvate dehydrogenase and by fatty acid oxidation cannot cross the mitochondrial membrane to participate directly in fatty acid synthesis. Instead, acetyl-CoA is linked with oxaloacetate to form citrate, which is transported from the mitochondrial matrix to the cytosol (Figure 25.1). Here it can be converted back into acetyl-CoA and oxaloacetate by ATP-citrate lyase. In this manner, mitochondrial acetyl-CoA becomes the substrate for cytosolic fatty acid synthesis. (Oxaloacetate returns to the mitochondria in the form of either pyruvate or malate, which is then reconverted to acetyl-CoA and oxaloacetate, respectively.)... 

FIGURE 25.1 The citrate-malate-pyruvate shuttle provides cytosolic acetate units and reducing equivalents (electrons) for fatty acid synthesis. The shuttle collects carbon substrates, primarily from glycolysis but also from fatty acid oxidation and amino acid catabolism. Most of the reducing equivalents are glycolytic in origin. Pathways that provide carbon for fatty acid synthesis are shown in blue pathways that supply electrons for fatty acid synthesis are shown in red. 

The strongest known producer of j8-poly(L-malic acid) has been identified as Aureobasidium sp. providing 61 g of polymer from 1 liter of culture medium [5,6]. 8-Poly(L-malate, Ca -salt) of the culture broth was first separated from accompanying bulk pullulan by methanol precipitation. The water-redisolved precipitate was converted to the polymer acid by passage over Amberlite IR-120B (H -form). Thus, the best to-day producers of... 

The purification of j8-poly(L-malic acid) from A o-basiae has been reported involving methanol precipitation of the polymer in the form of the Ca salt [5]. This is possible because a high concentration of CaCOs is present in the growth medium. Unfortunately, the polymer acid is not soluble in aceton thus missing an additional purification step. In our hands, purification of jS-poly(L-malate) from several Aureobasidiae strains was unsatisfactory because of low yields and resisting impurities. 

Infrared spectra and the degree of specific rotation show typical features of the malic acid polyester (Table 3). Ultraviolet absorbance spectra of )3-poly(L-malate) from both P. polycephalum and Aureobasidium sp, A-91 are similar and are reminiscent of malate itself [4,5]. For a solution of 1.0 mg/ml polymer, absorbance increases from 0.40 units at 230 nm to 10 units at 190 nm wavelength. After saponification and pH-neutralization, the absorbance increased from 8.7 units at 230 nm to 100 units at 190 nm. 

Alkaline (and also acidic) ester hydrolysis of /3-poly(L-malate) is accompanied by side reactions leading to the formation of fumarate, maleate and/or racemiza-tion, especially at elevated temperatures. The above assays thus underestimate the polymer contents due to the formation of small amounts of 2-4% fumarate (unpublished results). This fraction of fumarate increases for the hydrolysis of more concentrated polymer solutions. 

Poly(L-malate) decomposes spontaneously to L-ma-late by ester hydrolysis [2,4,5]. Hydrolytic degradation of the polymer sodium salt at pH 7.0 and 37°C results in a random cleavage of the polymer, the molecular mass decreasing by 50% after a period of 10 h [2]. The rate of hydrolysis is accelerated in acidic and alkaline solutions. This was first noted by changes in the activity of the polymer to inhibit DNA polymerase a of P. polycephalum [4]. The explanation of this phenomenon was that the degradation was slowest between pH 5-9 (Fig. 2) as would be expected if it were acid/base-catalyzed. In choosing a buffer, one should be aware of specific buffer catalysis. We found that the polymer was more stable in phosphate buffer than in Tris/HCl-buffer. 

Figure 2 Stability of /3-poly(L-malate) measured by its activity to inhibit purified DNA polymerase a of P. polyceph-alum. The relative degree of inhibition is shown (100 rel. units refer to complete inhibition). The DNA polymerase assay was carried out in the presence of 5 /tg/ml /S-poly(L-malate) as described [4]. The polymer was preincubated for 7 days at 4°C in the following buffer solutions (50 mM) KCl/HCl (—A—). Citrate (—V—). 2-(A/-Morpholino)-ethanesulfonic acid, sodium salt (—O—). Sodium phosphate (— —). N-(2-Hydroxyethyl)piperazine-N -(2-ethanesul-fonic acid), sodium salt (— — ). N,N-b s (2-Hydroxyethyl)-glycine, sodium salt (—T—). Tris/HCl (— —). 3-(Cyclo-hexylamino)-l-propanesulfonic acid, sodium salt (— —).

Figure 3 Reversed-phase chromatography of products after alkaline hydrolysis of /3-poly(L-malate), Discrete polymer products are formed, which differ in length by several units of L-malate. The absorbance at 220-nm wavelength was measured, (a) /3-Poly(L-malate) before hydrolysis, (b) After 10-min incubation in 20 mM NaOH at 37°C. (c) After 15 h in 20 mM NaOH at 37°C. (d) After I h in 500 mM NaOH at 100°C. High pressure chromatography (HPLC) on Waters reversed-phase Ci8- i-Bondapak. The methanol gradient (in water-trifluoro acetic acid, pH 3.0) was programmed as follows 0-40 min 0.3-23%, 40-47 min 23-40%, 47-49 min 40%, 49-54 min 40-0%. (d) Inset size exclusion chromatography after 3-min alkaline hydrolysis at pH 10.2. BioSil SEC 250 column of 300 mm x 7.8 mm size, 0.2 M potassium phosphate buffer pH 7.0.

Substantial amounts of polymalatase have been isolated from plasmodial extracts. This may refer to stored enzyme before secretion, because /3-poly(L-malate) is not degraded in plasmodia [24]. Several other fungi were found to secrete /3-poly(L-malate) degrading activities to L-malic acid (Ratberger, Molitoris and Holler, unpublished results). These enzymes have not yet been purified and characterized. 

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