Lactate formation

Bakken, I. J., White, L. R., Aasly, J. etal. Lactate formation from [U-13C] aspartate in cultured astrocytes compartmentation of pyruvate metabolism. Neurosci. Lett. 237 117-120, 1997. 

Alizade, M. A., Simon, H. Studies on mechanism and compartmentation of the L- and D-lactate formation from L-malate and D-glucose by Leuconostoc mesenteroides. Hoppe-Seylers Z. Physiol. Chem. 354, 163—168 (1973). 

Sodium fluoride (104) (1-10 mM) inhibits two enzymes of glycolysis the enolase (phosphopyruvate hydratase) and pyruvate kinase. Therefore, aerobic glucose utilization and lactate formation are blocked. 

It is these non-eqnilibrinm reactions that provide for the direction of glycolysis, i.e. that glycolysis from glycogen or glncose always proceeds in the direction of pyrnvate or lactate formation, i.e. it is these reactions that provide directionality in the pathway. The eqnilibrinm natnre of these reactions is discnssed from a kinetic viewpoint in Chapter 3. 

The equilibrium of the reaction strongly favors lactate formation. At high concentrations of lactate and NAD"", however, oxidation of lactate to pyruvate is also possible (see p. 18). LDH catalyzes the reaction in both directions, but—like all enzymes—it has no effect on chemical equilibrium. 

The overall equilibrium of this reaction strongly favors lactate formation, as shown by the large negative standard free-energy change. 

The transport system that conveys malate and a-ketoglu-tarate across the inner mitochondrial membrane (see Fig. 19-27) is inhibited by n-butylmalonate. Suppose n-butyl-malonate is added to an aerobic suspension of kidney cells using glucose exclusively as fuel. Predict the effect of this inhibitor on (a) glycolysis, (b) oxygen consumption, (c) lactate formation, and (d) ATP synthesis. 

In erythrocytes, external oxidants such as ferricyanide increase glycolysis (Harrison et al., 1991). Since these cells have no mitochondria, the increase in glycolysis could increase lactate or pyruvate formation, and excretion of these acids could be a basis for proton movement across the plasma membrane. In cells with mitochondria, the transmembrane electron transport decreases available NADH, so lactate formation would be decreased with consequent accumulation of pyruvate. The pyruvate... 

Activation of the glycolysis with lactate formation and/or lipogenesis, as shown in Fig. 6.7b. 

The first choice is lactate formation. The lactate concentration is typically increased by a factor of two or three during high glucose uptake [90]. Lactate is not only an escape route for surplus glucose uptake, but as most cells can take up lactate, it can then be oxidized or stored elsewhere. The signal for lactate formation is unknown. A possible candidate is G6P, which increases as the glycogen stores fill up. 

The cell free samples were mixed with perchloric acid/perchlorate and stored at low temperature for 48 h, at 6000 rpm centrifuged, decanted, stored at -22°C for a week and centrifuged again for deproteination. The separation was performed on an ion exclusion polystyrene/divinylbenzene column at 40 °C with 15 mM sulfuric acid as eluent and detection at 205 nm. For the quantification a standard was applied. A typical chromatogram is shown in Figure 6. Pyruvate, succinate, lactate, formate and acetate were detected in the cultivation medium. 

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