The calculation of ATP yield depends on the type of fatty acid being metabolized, specifically whether it has an even or odd number of carbon atoms. Here's a breakdown of the formulas and how to apply them, based on the provided reference:
Calculating ATP Yield from Fatty Acids
The reference gives specific formulas to calculate ATP yield from even and odd numbered fatty acids. These formulas take into account the carbon atoms present and the number of double bonds.
Key Parameters:
- C: Represents the number of carbon atoms in the fatty acid.
- D: Represents the number of double bonds in the fatty acid.
Formulas for ATP Yield:
-
Even-Numbered Fatty Acids:
The formula for calculating the ATP yield of even-numbered fatty acids is:
(7C - 6 - 1.5D) - 2(D-2)
- This formula accounts for the ATP produced from acetyl-CoA via the citric acid cycle and from NADH and FADH2 molecules via oxidative phosphorylation, also considering the energy cost of activating fatty acid.
-
Odd-Numbered Fatty Acids:
The formula for calculating the ATP yield of odd-numbered fatty acids is:
(7C - 19 - 1.5D) - 2(D-2)
- This formula takes into account the ATP generated from acetyl-CoA, propionyl-CoA, NADH and FADH2 while accounting for the energy cost of activating fatty acid and converting propionyl-CoA to succinyl-CoA.
Detailed Breakdown of the Formulas
| Component | Description | Contribution to ATP Yield (Even Fatty Acids) | Contribution to ATP Yield (Odd Fatty Acids) |
|---|---|---|---|
| 7C | This accounts for ATP generated from acetyl-CoA via the citric acid cycle and from NADH and FADH2 molecules via oxidative phosphorylation per 2 carbons from fatty acid catabolism | 7 ATP * C | 7 ATP * C |
| -6 or -19 | The energy cost of activating the fatty acid and the energy cost of converting propionyl-CoA to succinyl-CoA | -6 ATP | -19 ATP |
| -1.5D | This accounts for the reduction of ATP yield due to the presence of double bonds. | -1.5 ATP * D | -1.5 ATP * D |
| -2(D-2) | This accounts for the energy cost to isomerize the double bonds that are not in the beta position. | -2 ATP*(D-2) | -2 ATP*(D-2) |
Examples:
Let's illustrate with examples:
-
Palmitic Acid (C16, no double bonds):
- C = 16, D = 0
- Using the even-numbered formula: (7 16 - 6 - 1.5 0) - 2(0 - 2) = (112 - 6) - 2(-2) = 106 + 4 = 110 ATP
-
Oleic Acid (C18, 1 double bond):
- C= 18, D = 1
- Using the even-numbered formula: (718-6-1.51) - 2(1-2) = (126-6-1.5)-2(-1) = 118.5+2 = 120.5 ATP
- Note: The ATP yield is rounded off to 120 or 121.
-
Heptadecanoic Acid (C17, no double bonds):
- C = 17, D = 0
- Using the odd-numbered formula: (7 17 - 19 - 1.5 0) - 2(0 - 2) = (119 - 19) - 2(-2) = 100 + 4 = 104 ATP
Considerations
- These calculations provide theoretical ATP yields. Actual yields may vary due to cellular conditions.
- The formulas account for major metabolic pathways but might not include all minor regulatory effects.
- These formulas focus on fatty acid beta-oxidation and don't apply to other metabolic processes.
