Lactate redox potential

The right side of the illustration shows the way in which the redox potential E is dependent on the composition (the proportion of the reduced form as a %) in two biochemically important redox systems (pyruvate/lactate and NAD /NADH+H see pp.98, 104). In the standard state (both systems reduced to 50%), electron transfer from lactate to NAD" is not possible, because AE is negative (AE = -0.13 V, red arrow). By contrast, transfer can proceed successfully if the pyruvate/lactate system is reduced to 98% and NAD /NADH is 98% oxidized (green arrow, AE = +0.08 V). 

The key strategy when a new medium is developed is to reproduce the metabolic conditions of the cells when in vivo. Therefore, when adding media components it is important to maintain the pH, redox potential, and osmolality constant, as well as attempting to avoid generation of metabolic compounds that are toxic or growth inhibitory, such as lactate and/or ammonium. Apart from purely nutritional factors, it is important to develop a medium that is stable under normal storage conditions or in contact with light. 

Kidney damage results from precipitation of oxalate crystals in the convoluted tubules. The elevated anion-gap metabolic acidosis is caused by glycolic acid and lactic acid. The latter is formed from pyruvate due to a shift in the redox potential favoring the production of lactate. The treatment is the same as that for methanol intoxication. 

The enzyme, when isolated from a wide variety of sources, is specific for the A side of the nicotinamide ring 2 3,24). Organisms examined cover the range from mammals and plants (35) to bacteria (26,37). The A side specificity of the dogfish enzyme has been demonstrated by Biellmann and Rosenheimer (28). The )8-glycosidic bond is essential in both parts of the dinucleotide for activity (29). The redox potential of the pyridine nucleotide reaction is —0.320 V (30,31). Enzyme from a given species is specific either for d- or L-lactate. In some lower organisms such as horseshoe crab (32) and E. coli (33) the enzyme is specific for D-lactate, and there are indications that in these cases the active molecule is only a dimer (34). 

Relative initial rates of the dehydrogenation of (R)-lactate with various mediators determined with crude extracts of Proteus vulgaris (6,62). For preparative piuposes the redox potential of the applied mediator should be not more negative than -200 mV. 

Using pyruvate together with lactate dehydrogenase (LDH) to regenerate NAD" offers the advantage that LDH is less expensive and exhibits a higher specific activity than GluDH [753]. However, the redox potential is less favorable and LDH does not accept NADP". ... 

During the metabolism of the polyalcohols, the cytoplasmic NAD is largely reduced, as is demonstrated by elevation of the lactate/pyruvate ratio (Fig. 4). Addition of fructose caused only minor changes in this ratio and glucose was without any effect. Despite these changes in cytoplasmic redox potential, there was extensive glucose production from the sugars (see Fig. 3). 

Yeast mitochondrial flavocytochrome 2 (lactate cytochrome c oxido-reductase) catalyzes the transfer of electrons from L-lactate to various acceptors, cytochrome c being the physiological acceptor. The protoheme and flavin mononucleotide, because of their higher redox potential, can both be reduced completely by L-lactate the enzyme accepts a total of three electrons per protomer, which amounts to twelve electrons for the stable active tetramer. Both types of prosthetic group are quantitatively reoxidized by external acceptors. 

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