Glucose, aerobic oxidation phosphate

The PEP-fructophosphotransferase system does not exist in Spirillum itersoii, Pseudomonas aeruginosa,181,182 or several other genera of aerobic, oxidative bacteria.183 The transport system for D-glucose, D-fructose, and D-mannitol is energy- and temperature-dependent, obeys saturation kinetics, and is inducible.181,182 This indicates the presence of a carrier-mediated transport-system.184 D-Fructose is transported as the free sugar, and trapped intracellularly by phosphorylation, An inducible fructokinase (EC 2.7.1.4) converts transported D-fructose into D-fructose 6-phosphate.181... 

Disregarding proton leakage and assuming that the glycerol phosphate shutde is in operadon, 38 ATP would be produced from the aerobic oxidation of a glucose molecule. If the malate shutde is in operadon, only 36 ATP would be produced. 

The reaction rate will be at a maximum at a certain pH, owing to complex acid-base equilibria such as acid dissociation between the substrate, the activated complex, and the products. Also, the maximum rate may depend on the ionic strength and on the type of buffer used. For example, the rate of aerobic oxidation of glucose in the presence of the enzyme glucose oxidase is maximum in an acetate buffer at pH 5.1, but in a phosphate buffer of the same pH, it is decreased. 

Recent investigations indicate that synthesis of sucrose in plants is not accomphshed in the same way as in P. saccharophila. Despite numerous attempts, no enzyme system that would combine D-glucose-1-phosphate and D-fructose to form sucrose and inorganic phosphate could be isolated from the tissues of higher plants. However, biochemical studies on various species of plants support the view that the synthesis of sucrose may involve chemical reactions in which phosphate esters of both n-glucose and D-fructose serve as substrates. It is also significant that the experimental evidence shows that aerobic metabofism is indispensable for the synthesis of sucrose in the plant. Possibly aerobic oxidations are essential to the phosphorylation of one of the substrates involved in the synthesis. 

Figure 22.17 Summary of mechanisms to maintain the ATP/ADP concentration ratio in hypoxic myocardium. A decrease in the ATP/ADP concentration ratio increases the concentrations of AMP and phosphate, which stimulate conversion of glycogen/ glucose to lactic acid and hence ATP generation from glycolysis. The changes also increase the activity of AMP deaminase, which increases the formation and hence the concentration of adenosine. The latter has two major effects, (i) It relaxes smooth muscle in the arterioles, which results in vasodilation that provides more oxygen for aerobic ATP generation (oxidative phosphorylation). (ii) It results in decreased work by the heart (i.e. decrease in contractile activity), (mechanisms given in the text) which decreases ATP utilisation.

Fig. 8.2 Glycolysis and related pathways. Glycolysis is a central metabolic machinery in which one mole of glucose is catabolized to two moles of pyruvate, NADH, and ATP. Under aerobic conditions, pyruvate is further oxidized by mitochondrial system. In erythrocytes DHAP is a dead-end product however, in brain it can be converted into direction of lipid synthesis. Glycolysis and the pentose phosphate pathway (pentosePP) are interconnected via fructose-6-P and glyceral-dehyde-3-P. A high level of NADPH favors lipid synthesis via pentose phosphate shunt (pentosePP). At TPI inhibition (TPI deficiency), glyceraldehyde-3-Pcan be produced via G6PDH as well, to contribute to the glycolytic flux. a-GDH catalyzes the...

The answer is b. (Murray, pp 123-148. Scriver, pp 2367-2424. Sack, pp 159-175. Wilson, pp 287-317.) Aerobic glycolysis can be defined as the oxidative conversion of glucose to two molecules of pyruvate. In the process, two molecules of ATP and two molecules of NADH are produced. Since reducing equivalents from the two molecules of NADH produced in the cytoplasm must be transported into the mitochondrion for oxidation, it is not known how many ATP molecules are produced. On the assumption that two ATP molecules are formed per molecule of NADH oxidized via the glycerol phosphate shuttle, the ATP yield in aerobic glycolysis can be calculated as six ATP molecules per mole of glucose utilized. 

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