New mathematical derivations for calculation of ATP yield due to the complete oxidation of different types of fatty acids Banda Venkat Reddy1, (Published In Indian Journal of Biochemistry And Biophysics) Abstract
During complete oxidation of fatty acids, the electrons removed from fatty acids in different forms (FADH2 and NADH2) pass through the respiratory chain, driving the ATP synthesis. Generally, the total ATP yield due to the complete oxidation of fatty acids is calculated by sum of the ATPs obtained due to oxidation of FADH2 and NADH2. This calculation is simple for unsaturated even numbered fatty acids, but in case of saturated and unsaturated odd numbered fatty acids the calculation of ATP yield is difficult due to some changes in their β oxidation pathway when compared with β oxidation pathway of saturated even numbered fatty acids. For calculation of total ATPs produced due to the complete oxidation of different types (saturated, unsaturated, even numbered and odd numbered) of fatty acids, here we introduce the new mathematical formulas. , , ,
Keywords: Fatty acids, Respiratory chain, β Oxidation
Fatty acids are carboxylic acids with hydrocarbon chains ranging from 4 to 36 carbons long (C4 to C36)1,2. They are fuel molecules and are stored as triacylglycerols (also called neutral fats or triglycerides), which are uncharged esters of fatty acids with glycerol. Lipase converts triglycerides into free fatty acids. Fatty acids derived from triacylglycerols are oxidized to meet the energy needs of a cell or organism. Generally, the yield from the complete oxidation of one gram of fat is about 9 kcal g-1 (38 kJ g-1), in contrast with about 4 kcal g-1 (17 kJ g-1) for carbohydrates and proteins The oxidation of long-chain fatty acids to acetyl-coA is a central energy-yielding pathway in many organisms and tissues. In mammalian heart and liver, for example, it provides as much as 80% of the energy needs under all physiological circumstances. The complete oxidation of any fatty acid (e.g palmitic acid) to CO2 and H2O takes place in three stages: the oxidation of long chain fatty acids to two-carbon fragments in the form of acetyl CoA (β oxidation3) (Fig. 1), the oxidation of acetyl-CoA to CO2 in the citric acid cycle4,5, and the transfer of electrons from reduced electron carriers (FADH2 and NADH2) to the mitochondrial respiratory chain6-8 , resulting into the ATPs. Generally, the total ATP yield due to the complete oxidation of fatty acids is calculated by sum of the ATPs obtained due to oxidation of FADH2 and NADH2 as given in the following example. If palmitic acid undergoes complete oxidation, the total ATPs yield is calculated by the following steps9. Palmitic acid (16:0) undergoes β oxidation and gives the following products 8 Acetyl CoA +7 FADH2 + 7 NADH + H+ + AMP + PPi
7 FAD + 7 NAD+ + 7 CoASH + 7 H2O + H (CH2CH2)7CH2CO-SCoA --> 8 CH3CO-SCoA + 7 FADH2 + 7 NADH + 7 H+
If one acetyl CoA involved in TCA cycle gives = 10 ATPs
ATPs due to 8 acetyl-coA = 8 × 10 = 80 ATPs
ATPs due to 7 FADH2 = 1.5 × 7 = 10.5
ATPs due to 7 NADH + H+ = 2.5 × 7 = 17.5
Total No. of ATPs produced = 108
@For activation of fatty acid, one ATP is converted into AMP and Pi11 So, net ATPs produced = 108-2 = 106
These calculations assume that mitochondrial oxidative phosphorylation produces 1.5 ATP per FADH2 oxidized and 2.5 ATP per NADH2 oxidized. GTP produced directly in this step yields ATP in the reaction catalyzed by nucleoside diphosphate kinase12. This calculation is simple for unsaturated even numbered fatty acids, but in case of saturated and unsaturated odd numbered fatty acids, the calculation of ATP yield is difficult due to some changes in their beta- oxidation pathway (Figs 2 & 3) when compared with β oxidation pathway of saturated even numbered fatty acids. We have derived the following mathematical formulas for the same calculation for different types of fatty acids (saturated, unsaturated, even numbered and...
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