Lactate formation from glucose

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). 

R2 represents the cell growth (biomass formation) from glucose with inhibition by lactate. The biomass formed is converted into active cellular material. The reaction rates (i 3) and R4) describe the lactate and acrylic acid formation, respectively. 

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

How is it possible that both the glycolytic degradation of glucose to lactate and the reverse process, formation of glucose from lactate (gluconeogenesis), are energetically favorable ... 

A summary of the sources of ATP produced from one molecule of glucose is provided in Table 10.2. ATP production from fatty acids, the other important energy source, is discussed in Chapter 12. Several aspects of this summary require further discussion. Recall that two molecules of NADH are produced during glycolysis. When oxygen is available, the oxidation of this NADH by the ETC is preferable (in terms of energy production) to lactate formation. The inner mitochondrial membrane, however, is impermeable to NADH. Animal cells have evolved several shuttle mechanisms to transfer electrons from cytoplasmic NADH to the mitochrondrial ETC. The most prominent examples are the glycerol phosphate shuttle and the malate-aspartate shuttle. 

Equation (Rs) corresponds to the biomass formation from lactate, where a glucose inhibition term is included in the equation. Equation (R ) describes the formation of lactate dehydrogenase from active component in the cell material (X ). An acrylic acid inhibition term was added in this equation. Equation (Rt) shows the degradation rate of the active compartment and depends of the glucose and acrylic acid present in the medium. These reaction rates and the kinetic parameters values were obtained from Lei et al. [4] and modified to describe the acrylic acid production process. 

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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