(This post analise the energetic balance considering that the Propionyl CoA follows an anaplerotic fate)
Apply the equations described in the previous post:
N= Number of Carbons
(N/2) -1.5 = Number of rounds in Beta-oxidation
(N/2) -1.5 = Number of acetyl CoA produced in Beta-oxidation
So, in terms of production and consumption of ATP of ATPs, the oxidation of a 17-carbons fatty acid will show the following energetic balance:
Activation of a fatty acid to Acyl CoA = -2 ATP
Number of rounds in Beta-Oxidation:
(17/2) – 1.5 = 8.5 -1.5 = 7
7 rounds x 5 ATP/round = 35 ATP
Number of produced Acetyl CoA: 7 Acetyl CoA
7 Acetyl CoA x 12 ATP/Acetyl CoA = 84 ATP
Additionally, the Beta-oxidation has produced 1 Propionyl CoA. The conversion of Propionyl CoA to Succinyl CoA, as described in a former post, will consume 1 ATP (Consider -1 ATP).
As described in a previous post:
“We can consider the conversion of Propionyl CoA to Succinyl CoA as an anaplerotic pathway, in which case, the molecule of Succinyl CoA continue in the Krebs Cycle generating Oxalacetate in the following sequence of reactions:
Succinyl CoA + GDP + (P) —> Succinate + CoA + GTP (equivalent to 1 ATP)
Succinate + FAD ———-> Fumarate + FADH2 (Generates 2 ATPs in the Respiratory Chain)
Fumarate + H2O————– > Malate
Malate + NAD+ —————-> Oxalacetate + NADH.H+ (Generates 3 ATPs in the Respiratory Chain) “
Total = (-1+1+2+3) = 5 ATPs
Total of ATPs produced (considering the anaplerotic fate of the Propionyl CoA turned into Succinyl CoA) = -2+35+84-1+6 = 122 ATP
BUT…
We may also consider a total oxidation that would include the carbon atoms of the Propionyl CoA!
In our next post, we will consider what happens if, instead of the Succinyl CoA following an anaplerotic pathway, it follows a path that allow the carbon atoms of Propionyl CoA end up being oxidized to CO2. It would allow a real total oxidation of all the original carbons of the heptadecanoic acid or any other fatty acid with an odd number of carbons.
