Glycolysis and Fermentation

Anaerobic respiration only has two steps glycolysis and fermentation. Glycolysis again converts glucose into pyruvate. But in the absence of oxygen, fermentation converts pyruvate into ethanol, lactic acid, or a variety of other products, depending on the organism involved. 

Oxidative phosphorylation is the process by which NADH and FADHj are oxidized and ATP is produced. Two molecules of ATP are produced when FADHj is oxidized, and three molecules of ATP are produced when NADH is oxidized. The complete oxidation of one glucose molecule by glycolysis, the citric acid cycle, and oxidative phosphorylation yields thirty-six molecules of ATP versus two molecules of ATP for anaerobic degradation of glucose by glycolysis and fermentation. 

The first step in the physiological proteomics analysis of S. aureus is the establishment of a comprehensive two-dimensional (2D) gel proteome map that should cover most of the cytoplasmic proteins expressed under specific circumstances see Fig. 1). For physiological studies, the highly sensitive two-dimensional polyacrylamide gel electrophoresis (2D PAGE) originally invented by O Farrel (2) and Klose (3) is still the state of the art. With our standard 2D gel system (pH 4-7), we identified 473 proteins that cover about 40% of the cytoplasmic proteome of S. aureus predicted for this proteomic window (4). The proteins are associated with various cellular functions ranging from the transcriptional and translational machinery, citrate cycle, glycolysis, and fermentation pathways to biosynthetic pathways of nucleotides, fatty acids, and cell wall components (4,5). 

Diphosphoglyceric acid ( )dI- fas-fo-gli- Ser-ik- (1959) n. A diphosphate of glyceric acid that is an important intermediate in photosynthesis and in glycolysis and fermentation. 

In storage organs of other seeds a similar pattern of events can occur. In cotyledons (and embryos) of Cicer arietinum (chick-pea), enzymes of the glycolysis and fermentative pathways rise over the first 24 h after imbibition starts and then decline [41]. Enzymes of other pathways were not measured. In radish cotyledons, however, enzymes of the oxidative pentose phosphate pathway are present in the dry seed to a high level and rise even further over several days after imbibition. In contrast, the activity of the glycolytic enzyme phosphofructokinase never rises above the low level present in dry seed [108]. 

Discuss the cycling of NADH and NAD in glycolysis and the related fermentation reactions. 

Yeast and other microorganisms ferment glucose to ethanol and C02, rather than to lactate. Glucose is converted to pyruvate by glycolysis, and the pyruvate is converted to ethanol and C02 in a two-step process ... 

When plants experience anoxic conditions there is a shift in carbohydrate metabolism from an oxidative to a fermentative pathway (Fig. 1). In the absence of oxygen, ATP is generated not by the Krebs cycle but by alcoholic fermentation, i.e. glycolysis and ethanol synthesis. 

K. Burton and H. A. Krebs, The free energy changes associated with the individual steps of the tricarboxylic acid cycle, glycolysis, alcoholic fermentation, and with the hydrolysis of the pyrophosphate group of adensosine triphosphate, Biochem.. /. 54, 94-107 (1953). 

But even if a combination of pathways usually is used, the ATP yield can nevertheless be elevated two- to fourfold any animal anaerobes utilizing such fermentations therefore automatically reduce by a factor of two to four their anaerobic needs for glucose. Although impressive, this factor is still a long way from the order-of-magni-tude difference between anaerobic glycolysis and oxidative glucose metabolism. 

It is clear that phosphate is required for the continued operation of glycolysis and ethanol formation. In extracts to which glucose is added, fermentation proceeds until ADP and P4 (present in the extracts) are exhausted. 

This metabolic scheme, which is called lactate fermentation, is shown in Fig. 11-7. The coreactant cycle between the two dehydrogenase enzymes, glyceraldehyde-3-phosphate dehydrogenase (Step 6) and lactate dehydrogenase, ensures that there is regeneration of NAD+ in this particular oxidation state so that glycolysis, lactate fermentation, and the production of ATP can continue. 

NADH peroxidase (Npx EC 1.11.1.1) and NADH oxidase (Nox EC 1.6.99.x) are disulfide oxidoreductases-related enzymes that contain a single redox-active cysteine (16). They supply strictly fermentative bacteria with NAD+ for glycolysis and play an important role in redox signaling in response to oxidative and nitrosative stress (19). 

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