Malate, determination

G.C. Chemnitius, R.D. Schtnid, L-Malate determination in wines and fruit juices by flow injection analysis adaptation of coupled dehydrogenase/transferase system, Anal. Lett. 22 (1989) 2897. 

Malate, determination of 62-65 Maleate, determination of 60-65, 212 Malonate, determination of 60-62, 213 Manganese, determination of 229 Mercaptobenzthiazole, determination of 133... 

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 bioluminescent determinations of ethanol, sorbitol, L-lactate and oxaloacetate have been performed with coupled enzymatic systems involving the specific suitable enzymes (Figure 5). The ethanol, sorbitol and lactate assays involved the enzymatic oxidation of these substrates with the concomitant reduction of NAD+ in NADH, which is in turn reoxidized by the bioluminescence bacterial system. Thus, the assay of these compounds could be performed in a one-step procedure, in the presence of NAD+ in excess. Conversely, the oxaloacetate measurement involved the simultaneous consumption of NADH by malate dehydrogenase and bacterial oxidoreductase and was therefore conducted in two steps. 

The practical usefulness of Equations 11.46 through 11.53 has been demonstrated for the malic enzyme catalyzed conversion of L-malate to pyruvate (Equation 11.72). Table 11.1 lists experimentally determined isotope effects for this reaction. Comparison of carbon kinetic isotope effects for protio and deutero-malate substituted at position 2 (the carbon that undergoes sp3 to sp2 transition) rules out the possibility that the hydride transfer and the decarboxylation events are concerted. This conclusion follows from Equation 11.48 which, for a concerted reaction, predicts that 13(V/K) should be smaller than 13(V/K)D, which is opposite to the order observed experimentally. 

Fig. 7. Enzyme-coupled assay in which the hydrolase-catalyzed reaction releases acetic acid. The latter is converted by acetyl-CoA synthetase (ACS) into acetyl-CoA in the presence of (ATP) and coenzyme A (CoA). Citrate synthase (CS) catalyzes the reaction between acetyl-CoA and oxaloacetate to give citrate. The oxaloacetate required for this reaction is formed from L-malate and NAD in the presence of L-malate dehydrogenase (l-MDH). Initial rates of acetic acid formation can thus be determined by the increase in adsorption at 340 nm due to the increase in NADH concentration. Use of optically pure (Ry- or (5)-acetates allows the determination of the apparent enantioselectivity i app i81)-...

Ca salts differ from one another in terms of the anions and molecules that they are associated with. CCM s characteristic aqueous solubility is directly related to the citrate and malate anions. The in vitro solubility of any Ca salf is essenfially constant under standard conditions (e.g., at neutral pH in water). Once a Ca source is consumed, it encoimters a host of variable environmental factors, such as pH changes, interactions with other food components, and the hormonal milieu, that alter its solubility and/or potential for absorption. It is the net impact of these internal factors, together with the combination of introduced variables, such as the food matrix in which Ca is incorporated and the timing of Ca intake, that contribute to determining just how beneficial to health a Ca source will be. 

The cadmium complexes were also investigated potentiometrically. Using this method, the complexes of cadmium with asparagine [128], taurine [129], A -(6-ami-no-3-methyl-5-nitroso-4-oxo-3,4-dihydro-pyrimidin-2-yl)glycine [130], succinate and malate [131], acetate at different temperatures [132], pyridine oxime ligands [133], 2-hydroxypropene-l,3-diamine-Af,Af,Af, A -tetraacetic acid [134] were studied. The stoichiometry and stability constants of these complexes were determined. 

Determination of the absolute configurations of the 3,6-dideoxy-hexoses involved their degradation, according to Scheme 2, to malic acid, and identification of the latter acid with L-malate dehydrogenase.56 The anomeric configuration in 9—12 was assumed to be the same... 

Malic Acid. This is seldom determined quantitatively in winery practice. However, qualitative paper chromatography is often done to follow malo-lactic fermentation. Using n-butyl alcohol and formic acid (80), the Rf values are tartaric 0.28, citric 0.45, malic 0.51, ethyl acid tartrate 0.59, lactic acid 0.78, succinic 0.78, and ethyl acid malate 0.80. 

However, it has become clear that protons removed from a substrate to a basic group in a protein need not exchange rapidly with solvent (see Eq. 9-102). In fact, the proton removed by fumarate hydratase from malate is held by the enzyme for relatively long periods of time. Its rate of exchange between malate and solvent is slower than the exchange of a bound fumarate ion on the enzyme surface with another substrate molecule from the medium.59 Thus, the overall rate is determined by the speed of dissociation of products from the enzyme and we cannot yet decide whether removal of a proton precedes or follows loss of OH. ... 

A key structural and mechanistic feature of lactate and malate dehydrogenases is the active site loop, residues 98-110 of the lactate enzyme, which was seen in the crystal structure to close over the reagents in the ternary complex.49,50 The loop has two functions it carries Arg-109, which helps to stabilize the transition state during hydride transfer and contacts around 101-103 are the main determinants of specificity. Tryptophan residues were placed in various parts of lactate dehydrogenase to monitor conformational changes during catalysis.54,59,60 Loop closure is the slowest of the motions. 

If a method similar to Dionex application no. 123 is used, both organic acids and anions can be separated on the AS-11 column (Figure 10.8) (Anon, n.d.e). In fact, care has to be taken with this method as nitrate and malate ions elute very close to each other under these conditions. This can be a particular issue if the column is not operating well and there is a need to determine the level of nitrate in juices which contain high levels of malic acid. 

A suspension of mitochondria is incubated with pyruvate, malate, and l4C-labeled triphenylmethyl-phosphonium [TPP] chloride under aerobic conditions. The mitochondria are rapidly collected by centrifugation, and the amount of l4C that they contain is measured. In a separate experiment, the volume of the mitochondrial matrix space was determined so that the concentration of TPP cation in the matrix can be calculated. The internal concentration is found to be 1,000 times greater than that in the external solution. 

The problem of stepwise versus concerted oxidative decarboxylation of L-maleate to yield pyruvate CO2 and reduced dinucleotide catalysed by malic enzyme615 has been reinvestigated recently616. The new D and T KIE determinations, using L-malate-2D... 

The text-book Walden-style cycle which interconverts the stereochemical configurations of chlorosuccinate (3) and malate (5) involves a /3-lactone intermediate (2) in preference to an a-lactone intermediate (4) (Scheme 2) because the OnUc-C-Cl angle in the transition structure for the former (174°) is more favourable than that for the latter (139°), as determined by PCM(e = 78.4)/B3LYP/6-31+G calculations the smaller ring-strain energy of the /3-lactone contributes little to the reactivity difference.2 (V,A-Dimethylethanolamine esterified hexanoic acid about 10-fold faster than did hexanol as a consequence of intermolecular hydrogen bonding a seven-membered transition state (6) was proposed.3... 

Because of the rapid rotation of the methyl group in CHDTC02H, the question as to whether H, D or T is abstracted in the formation of the carbanion or carbanionoid intermediate in the aldol condensation to give malate is not determined stereo-... 

With the stereochemistry of the citrate lyase reaction determined, that of the Si citrate synthetase (the common enzyme) was established as shown in Fig. 70. Condensation of (J )-acetic-d, t acid (configuration known by synthesis) with oxalo-acetate gives what turns out to be mainly (2S,3/ )-citric-2-d,2-/ acid (112).41 When this acid is then cleaved with citrate lyase, the major product is (/ )-acetic-d, t acid, as established by the malate synthetase/fumarase diagnosis. It follows that both the Si-citrate synthetase and citrate lyase reactions must involve the same stereochemical course. Since that of the lyase reaction is inversion (vide supra), that of the Si synthetase reaction must be inversion also. And since the overall stereochemical result shown in Fig. 70 is not dependent on the magnitude of the... 

The protonation constants and the binding constants with different chiral carboxylates have been determined by means of pH-metric titrations. The triprotonated form of (S,S,S,S)-6 showed moderate enantioselectivity with malate and tartrate anions (AAG=0.62 and 0.66 kcal/mol, respectively), the strongest binding being observed in both cases with the L-enantiomer. Good enantiomeric discrimination was obtained with tetraprotonated (R,R)-5 and... 

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