Lactate pyruvate reduction

FIGURE 19.30 (a) Pyruvate reduction to ethanol in yeast provides a means for regenerating NAD consumed in the glyceraldehyde-3-P dehydrogenase reaction, (b) In oxygen-depleted muscle, NAD is regenerated in the lactate dehydrogenase reaction. 

LDH. Rather surprisingly, the properties of LDH have been investigated fully only in Hymenolepis spp. Burke et al. (108) purified 128-fold a single species of LDH from H. diminuta which resembled the H form of mammalian LDH. Other workers (448, 567, 630, 926) were able to distinguish electrophoietically at least two LDH isoenzymes in H. diminuta and H. microstoma. The kinetic parameters for LDH, similar in both species (Table 5.7), indicate that pyruvate reduction is favoured over lactate oxidation and that pyruvate, once formed, would be rapidly reduced to lactate, with the subsequent oxidation of NADH. 

Oxidation of lactate to pyruvate is inhibited, leading to a reduction in gluconeogenesis and accumulation of lactate (pyruvate + NADH + H — lactate + NAD ). 

As previously mentioned (p. 7), bacteria like S. oneidensis and G. metallireducens have the capacity to reduce insoluble Mn02 to soluble Mn + enzymatically by anaerobic respiration with a suitable electron donor in a direct process in which the respective organisms attach to the surface of the oxide. In the case of S. oneidensis, the electron donor may be lactate, pyruvate, formate or H2, but not acetate. The lactate and pyruvate are oxidized to acetate as end-product. Geobacter metallireducens can use butyrate, propionate, lactate and acetate as electron donors, but not H2 or formate, and oxidizes the organic electron donors completely to CO2 and H2O. Geobacter sulfurreducens can use H2 as electron donor in Mn02 reduction (see Lovley, 2000). 

With a constant of K = 2.7640-5 mol/1 (pH 7.0, 25°C) the equilibrium of the LDH-catalyzed reaction lies far to the lactate side. This means that whereas for lactate sensors based on LDH the forward reaction has to be forced by alkaline buffer and pyruvate- or NADH-trapping agents, the reduction of pyruvate proceeds spontaneously under normal conditions. This direction of the reaction has been used in a sequence electrode for pyruvate assay (Weigelt et al., 1987b). In the presence of lactate monooxygenase (LMO) lactate formed from pyruvate by LDH is oxidized by molecular oxygen, the consumption of which was indicated at a Clark-type electrode. The enzymes were immobilized in a gelatin membrane. Of course such a sensor measures the concentration of lactate in the sample, too. Therefore it is suited to the determination of the lactate/pyruvate ratio, which is a clinically important parameter. Pro-... 

Pig heart Lactate DH -17.5 -11.6 0.9 Glyoxalate reduction Pyruvate reduction/lactate oxidation Glyoxalate oxidation 430 192/85 115 Rel 71... 

Similar studies of the enzyme from pig skeletal muscle have been reported 175,183). In the earlier work, a fast burst of NADH formation in the dead-time of the apparatus was observed, equal in amplitude to the active center concentration at pH 8.0, but smaller at lower pH values. The suggestion that slow isomerization of the ternary product complex before pyruvate release may be the step responsible for the low steady-state maximum rate of lactate oxidation seems to be inconsistent with the full burst observed at pH 8.0, since it might be expected to result in partial equilibration of the reactant and product ternary complexes. Direct studies of the oxidation of E-NADH by pyruvate at pH 9.0 did indicate that reverse hydride transfer from NADH to pyruvate is indeed fast, but the absence of a deuterium isotope effect suggested that the observed rate constant of 246 sec, equal to the maximum steady-state rate of pyruvate reduction, may reflect an isomerization of the ternary complex preceding even faster hydride transfer. More recent studies 183) with improved techniques, however, appear to indicate no burst of enzyme-bound NADH formation preceding the steady-state phase of lactate oxidation at pH 8.0. On the basis of stopped-flow studies of lactate oxidation in the presence of oxamate, which forms a dead-end complex with E-NADH and can serve as an indicator of the rate of formation... 

Oxidation is favored over reduction during hypoglycemia, and all cellular redox pairs tilt their reactions toward oxidation in hypoglycemia. Thus, lactate/pyruvate, NAD/NADH, GSG/GSSG and NADP/NADPH all shift their equilibria toward the oxidized compound of the pair (Agardh et al., 1978). Whether the oxidized cellular state of hypoglycemia leads to oxidative damage to DNA or proteins is still unknown. 

HEAR oil and peanut oil. They concluded that dietary fat did not alter mitochondrial function. Lactate/pyruvate ratio, however, does not necessarily reflect the state of oxidation/reduction of cytoplasmic NADH (Olson, 1963). 

Accumulation of compounds related to the mitochondrial pathway can be detected in one or more body fluids of most patients [1, 2, 15]. Special attention has to be paid to the lactate concentration. Excess of lactate and alanine will be produced after reduction or transamination of accumulated pyruvate (see Fig. 27.1). If there is a severe block in the pyruvate oxidation pathway, and the produced lactate can not adequately be removed by peripheral tissues, it accumulates in blood, urine and/or cerebrospinal fluid, dependent upon the affected tissue(s). A decreased activity of the respiratory chain will shift the equilibrium of the lactate dehydrogenase reaction to conversion of pyruvate to lactate (see also Sect. 1). Thus, patients with a respiratory chain defect should demonstrate an increased lactate/pyruvate ratio in blood, whereas pyruvate dehydrogenase deficiency should result in a normal lactate/pyruvate ratio. However, this tool for differential diagnosis is not helpful in all cases. Furthermore, some patients do not accumulate lactate in blood or urine. 

Enzyme catalyzed reductions of carbonyl groups are more often than not com pletely stereoselective Pyruvic acid for example is converted exclusively to (5) (+) lactic acid by the lactate dehydrogenase NADH system (Section 15 11) The enantiomer... 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

Finally in this section on deracemization via cyclic oxidation/reduction methods, there has been some limited work carried out on the deracemization of secondary alcohols. Soda et al. [22] employed lactate oxidase in combination with sodium borohydride to deracemize D/i-lactate (18) via the intermediate pyruvate (19) (Figure 5.12). 

Bacteria have been isolated using reduced anthraquinone-2,6-disulfonate (HjAQDS) as electron donor and nitrate as electron acceptor (Coates et al. 2002). The organisms belonged to the a-, p-, y-, and 5-subdivision of the Proteobacteria, and were able to couple the oxidation of H AQDS to the reduction of nitrate with acetate as the carbon source. In addition, a number of C2 and C3 substrates could be used including propionate, butyrate, fumarate, lactate, citrate, and pyruvate. 

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