Pyruvate from glucose

For each molecule of glucose formed from pyruvate, six high-energy phosphate groups are required, four from ATP and two from GTP. In addition, two molecules of NADH are required for the reduction of two molecules of 1,3-bisphosphoglycerate. Clearly, Equation 14-9 is not simply the reverse of the equation for conversion of glucose to pyruvate by glycolysis, which requires only two molecules of ATP ... 

We saw in Chapter 14 that the energy yield from the production of two molecules of pyruvate from one molecule of glucose in glycolysis is 2 ATP and 2 NADH. In oxidative phosphorylation (Chapter 19), passage of two electrons from NADH to 02 drives the formation of about 2.5 ATP, and passage of two electrons from FADH2 to 02 yields about 1.5 ATP. This stoichiometry allows us to calculate the overall yield of ATP from the complete... 

FIGURE 18-9 Glucose-alanine cycle. Alanine serves as a carrier of ammonia and of the carbon skeleton of pyruvate from skeletal muscle to liver. The ammonia is excreted and the pyruvate is used to produce glucose, which is returned to the muscle. 

Why is lactate formed from pyruvate in the metabolism of glucose Pyruvate... 

Pyruvate, from glycolysis of glucose, is carboxylated to oxaloacetate or oxidized to acetyl-CoA. These metabolites enter the Krebs cycle, are metabolized to a-ketoglutarate and oxaloacetate, then transaminated to aspartate or glutamate. Asn, Gin, and Pro are synthesized from Asp or Glu. The cycle replenishes intermediates via the anaplerotic reactions (e.g., car-boxylation of pyruvate to form oxaloacetate). 

Fed-batch production of pyruvic acid [CH3COCOOH] from an engineered strain (Escherichia coli YYC202) was optimized by resorting to ED to prevent potential product inhibition in the bioreactor (Zelic et al., 2004). In this way, by continuous separation of pyruvate from the fermentation medium, high values of the pyruvate-to-glucose molar yield (1.78 mol/mol), volumetric productivity (145 kg m 3day ), and pyruvate concentration (79 kg/m3) were achieved by the repeated fed-batch mode. 

Figure 10-1. Enzymatic pathways for glucose synthesis from amino acids or pyruvate in mammalian Ever. Enclosed in the boxes are the glucogenic amino acids with arrows indicating the points where carbon skeletons from these amino acids enter the pathways of gluconeogenesis or the tricarboxylic acid cycle. Bracketed next to the rate-controlling enzymes for gluconeogenesis are some of the substances that increase (T) or decrease (1) the activity of these enzymes. 3PG, 3-phosphoglycerate.

The production of two molecules of pyruvate from one molecule of glucose occurs in virtually all cells. This process has three important characteristics (1) no oxygen is required (2) two molecules of ADP are phosphorylated by substrate-level phosphorylation and (3) two molecules of NAD+ are reduced. The subsequent fate of pyruvate in a particular cell depends on conditions related to these... 

The chart overleaf shows the molecules of primary metabolism and the connections between them, and needs some explanation. It shows a simplified relationship between the key structures (emphasized in large black type). It shows their origins—from CO2 in the first instance—and picks out some important intermediates. Glucose, pyruvic acid, citric acid, acetyl coenzyme A (Acetyl Co A), and ribose are players on the centre stage of our metabolism and are built into many important molecules. 

Figure 4.23 illustrates the patterns tif metabolism in the liver In muscle, the directions of nutrient Eux at points (1) and (3) are opposite those shown that is, glucose derived from the bloodstream is converted to G-6-I then to pyruvate. TTiis pyruvate can then be completely oxidi2ed in the mitochondria or can enter the bloodstream in the form of lactate. Muscle does not contain glucose-6 phosphatase and thus cannot export glucose units stored as muscle glycogen. 

Figure 19-1 a Normal and ischemic myocardial metabolism of glucose. A total production of 36 moles of ATP results from the aerobic catabolism of 1 mole of glucose and use of NADH and FADH. in the oxidative phosphorylation process in mitochondria. When oxygen is not available, NADH and FADH levels rise and shut off the tricarboxylic acid (TCA) cycle. Pyruvate is converted to lactate. Only 2 moles of ATP are formed from anaerobic catabolism of 1 mole of glucose. (Adapted from Giuliani, E. R., ei al. Cardiology Fundamentals and Practice, 2nd ed. By permission of the Mayo Foundation, Rochester, MN.)... 

---