Metabolism and ATP yield

Here n = 6, and ATP yield per mole glucose is 6 x 6 = 36. AG 0 = —108 x 6 = -648 kcal. In reality, because each mole of ATP (hydrolyzed to ADP) is worth only 8.4 kcal/M, the oxidation of glucose yields only 302 kcal. The other 346 kcal is wasted as heat. The metabolic engine is therefore only about 47% efficient, which for engines is excellent. 

Note The.se P/O ratios of 2.5 and 1.5 for mitochondrial oxidation of NADH and [FADHg] are consen.sns values. Because diey may not reflect actual values and because these ratios may change depending on metabolic conditions, the.se estimates of ATP yield from glucose oxidation are approximate. 

Lactate versus Alanine as Metabolic Fuel The Cost of Nitrogen Removal The three carbons in lactate and alanine have identical oxidation states, and animals can use either carbon source as a metabolic fuel. Compare the net ATP yield (moles of ATP per mole of substrate) for the complete oxidation (to C02 and H20) of lactate versus alanine when the cost of nitrogen excretion as urea is included. 

It is now evident that at least two, and probably more, of the four possible reductive steps are coupled to ATP formation in denitrifying bacteria. As may be expected from thermodynamic consideration, this crucial observation implies an ATP yield per mole of glucose similar to that for normal oxidative metabolism (see Gottschalk, 1979, for literature in this area). 

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. 

Pantothenic acid has a central role in energy-yielding metabolism as the functional moiety of coenzyme A (CoA), in the biosynthesis of fatty acids as the prosthetic group of acyl carrier protein, and through its role in CoA in the mitochondrial elongation of fatty acids the biosynthesis of steroids, porphyrins, and acetylcholine and other acyl transfer reactions, including postsynthetic acylation of proteins. Perhaps 4% of all known enzymes utilize CoA derivatives. CoA is also bound by disulfide links to protein cysteine residues in sporulating bacteria, where it may be involved with heat resistance of the spores, and in mitochondrial proteins, where it seems to be involved in the assembly of active cytochrome c oxidase and ATP synthetase complexes. 

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