Stearic acid energy yield

It is instructive to compare the energy yield from three molecules of glucose (Cig) with that from one molecule of stearic acid (also Cig). 

In carbohydrate metabolism, the energy released by oxidation reactions is used to drive the production of ATP, with most of the ATP produced in aerobic processes. In the same aerobic processes—namely, the citric acid cycle and oxidative phosphorylation—the energy released by the oxidation of acetyl-GoA formed by P-oxidation of fatty acids can also be used to produce ATP. There are two sources of ATP to keep in mind when calculating the overall yield of ATP. The first source is the reoxidation of the NADH and FADHg produced by the P-oxidation of the fatty acid to acetyl-GoA. The second source is ATP production from the processing of the acetyl-GoA through the citric acid cycle and oxidative phosphorylation. We shall use the oxidation of stearic acid, which contains 18 carbon atoms, as our example. 

The activation step in which stearyl-GoA was formed is not included in this calculation, and we must subtract the ATP that was required for that step. Even though only one ATP was required, two high-energy phosphate bonds are lost because of the production of AMP and PPj. The pyrophosphate must be hydrolyzed to phosphate (Pj) before it can be recycled in metabolic intermediates. As a result, we must subtract the equivalent of two ATP for the activation step. The net yield of ATP becomes 120 moles of ATP for each mole of stearic acid that is completely oxidized. See Table 21.1 for a balance sheet. Keep in mind that these values are theoretical consensus values that not all cells attain. 

What is the energy yield from the oxidation of fatty acids There is a net yield of 120 ATP molecules for each molecule of stearic acid (an 18-carbon compound) that is completely oxidized to carbon dioxide and water. The source of these ATP molecules is the production of NADH and LADHg in the P-oxidation pathway, as well as the NADH, LADHg, and GTP produced when the acetyl-GoA molecules are processed through the electron transport chain. 

Recall Compare the energy yields from the oxidative metabolism of glucose and of stearic acid. To be fair, calculate it on the basis of ATP equivalents per carbon and also ATP equivalents per gram. 

To compare the energy yield from fatty acids with that from glucose, let s continue our discussion with stearic acid, a typical and abundant fatty acid. 

Figure 4 Mechanical properties of compounds containing stearic acid coated calcium carbonate in polyethylene (a) tensile yield stress (b) impact energy using instrumented falling weight impact tester.

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