Oxalacetate malate

There are also voices critical of the rTCA cycle Davis S. Ross has studied kinetic and thermodynamic data and concludes that the reductive, enzyme-free Krebs cycle (in this case the sequence acetate-pyruvate-oxalacetate-malate) was not suitable as an important, basic reaction in the life evolution process. Data on the Pt-catalysed reduction of carbonyl groups by phosphinate show that the rate of the reaction from pyruvate to malate is much too low to be of importance for the rTCA cycle. In addition, the energy barrier for the formation of pyruvate from acetate is much too high (Ross, 2007). 

Other redox systems of importance in biochemistry include the NADH/NAD system, the flavins, the pyruvate/lactate system, the oxalacetate/malate system, and the quinone/hydroquinone system. 

Malate/oxalacetate Malate dehydrogenase/Lactate monooxygenase Oxygen electrode... 

Biotin is a growth factor for many bacteria, protozoa, plants, and probably all higher animals. In the absence of biotin, oxalacetate decarboxylation, oxalosuccinate carboxylation, a-ketoglutarate decarboxylation, malate decarboxylation, acetoacetate synthesis, citrulline synthesis, and purine and pyrimidine syntheses, are greatly depressed or absent in cells (Mil, Tl). All of these reactions require either the removal or fixation of carbon dioxide. Together with coenzyme A, biotin participates in carboxylations such as those in fatty acid and sterol syntheses. Active C02 is thought to be a carbonic acid derivative of biotin involved in these carboxylations (L10, W10). Biotin has also been involved in... 

Metal amalgams may be used for reduction of the keto groups in keto esters provided the medium does not cause hydrolysis of the ester. Because of that aluminum amalgam in ether is preferable to sodium amalgam in aqueous solutions. Diethyl oxalacetate was reduced to diethyl malate by sodium amalgam in 50% yield and with aluminum amalgam in 80% yield [148], Stereospecific reduction of a- and fi-keto esters to optically pure hydroxy esters was achieved by biochemical reduction in moderate to good yields. Saccharomyces cerevisiae converted methyl 2-keto-2-phenylacetate to methyl... 

Lactate, glycolate, succinate, chloride, malate, sulphate, tartrate, maleate, fluoride, a-hydroxybutyrate, hydroxy valerate, formate, valerate, pyruvate, monochloroacetate, bromate, galaconurate, nitrite, gluconurate, dichloroacetate, trifluoroacetate, hypophosphite, selenite, bromide, nitrate, oxalate, selenate, a-ketoglutarote, fumarate, phthalate, oxalacetate, phosphate, arsenate, chromate, citrate, isocitrate, cis aconitate and transaconitrate... 

The subsequent conversion of oxalacetate to succinate is believed to occur by way of malate and fumarate since Krebs and Eggleston have demonstrated that the following reactions occur reversibly in propionic acid bacteria. 

Further proof that COj is assimilated by means of the enzyme oxalacetate /3-carboxylase was obtained by Evans and coworkers, who succeeded in preparing a cell-free preparation of this enzyme from liver. The enz3rme was able to catalyze the decarboxylation of oxalacetate to pyruvate. These investigators were able to demonstrate an uptake of C Oj. Utter and Wood have demonstrated conclusively, however, that in the presence of isotopic CO2, pyruvate can be converted to oxalacetate containing isotopic carbon and that the process is, of course, reversible. Addition of adenosine triphosphate to this liver enzyme system increased the rate of incorporation of C Os. Wood, Vennesland and Evans S have also shown that during the fixation of C02, isotopic carbon is incorporated solely and in equal concentrations into the carboxyl groups of pyruvate, lactate, malate and fumarate. 

COs to form oxalacetate which under anaerobic conditions is reduced to malate. The malate in turn may be converted to fumarate and succinate (Fig, 5). The last step in this series of reactions is blocked by malonate. The second pathway involves the aerobic condensation of pyruvate and oxalacetate followed by oxidation of the condensation product to form -ketoglutarate and succinate. Wood has proposed that the first condensation product of the aerobic tricarboxylic cycle is cfs-aconitic acid which is then converted to succinate by way of isocitric, oxalosuccinic, and a-ketoglutaric acids. The a-ketoglutarate is decarboxylated and oxidized to succinic acid. Isotopic a-ketoglutarate containing isotopic carbon only in the carboxyl group located a to the carbonyl would be expected to yield non-isotopic succinate after decarboxylation. This accounts for the absence of isotopic carbon in succinate isolated from malonate-poisoned liver after incubation with pyruvate and isotopic bicarbonate. 

Both are abundant in skeletal muscle, myocardium, liver, and erythrocytes, so that hemolysis must be avoided, and in serum they may be assayed spectrophotometrically by their conversion of phosphate-buffered pyruvate to lactate (R6, W16) or oxalacetate to malate (S25) at the expense of added NADH2, when the rate of decrease of optical density at 340 m x thus measmes the serum activities of the respective enzymes. Recently, however, the reverse reaction has been found best for serum lactic dehydrogenase assay (A2a). In conventional spectrophotometric units the normal ranges are 100-600 units per ml for lactic dehydrogenase (W16) and 42-195 xmits per ml for malic dehydrogenase (S25) as before, one conventional spectrophotometric unit per ml = 0.48 pmoles/ minute/liter (W13). 

Dehydrogenase activity of MDH was suppressed by NADH at 5% of the NAD concentration. Oxidative activity of ADH was suppressed when NADH approached the concentration of NAD. The reductase activities were not suppressed by NAD at even 10 times the concentration of NADH. The increase in the redox ratio in senescing and anaerobic citrus fruit could inhibit the oxidation of malate to oxalacetate and increase the flux via the decarboxylation pathway through pyruvate to ethanol (Figure 1). 

Creighton and Rose (45) have explored the route shown in Scheme 7 to synthesize chiral pyruvate. The method takes advantage of the fact that pyruvate kinase decarboxylates oxalacetate with retention of configuration. The requisite labeled oxalacetates were prepared as shown from the appropriately labeled L-malates, available from equilibration with fumarase in either deuterated or tritiated water. This method is convenient for the preparation of small amounts of chiral acetate but suffers from the low oxalacetate decarboxylase activity of pyruvate kinase. 

Dehydrogenase, malate (oxalacetate-decarboxylating) (nicotinamide adenine dinucleotide phosphate) 429b, 922a, 4249... 

Another interesting approach to the less readily accessible diethyl ( S)-malate (3) is enan-tioselective bioreduction of sodium diethyl oxalacetate (4) with baker s yeast Saccharomyces cerevisiae). Under fermenting conditions, 3 is produced in high yield with >98% ee [10]. 

Aminooxyacetate, an inhibitor of glutamate— oxalacetate transaminase, inhibits the formation of aspartate. Soling Kleinicke (1976) observed that aminooxyacetate did not inhibit the formation of glucose from lactate and, therefore, concluded that the malate-aspartate shuttle was not essential for the lactate gluconeogenesis in avian liver. However, Ochs Harris (1980) found that aminooxyacetate did block lactate gluconeogenesis when lower concentrations of pyruvate were used and incubation was for longer than 15 min. They concluded that the malate-aspartate shuttle was required. 

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