4. Margaric acid (heptadecanoic acid, an unbranched C17:0 fatty acid) is a fairl

Question

4. Margaric acid (heptadecanoic acid, an unbranched C17:0 fatty acid) is a fairly rare fatty acid that was first reported in 1957 to be found, in trace amounts, in fat of mutton and in fat and butterfat of other ruminants. A) What is the net yield of ATP for the complete metabolic conversion of margaric acid to CO2? Clearly illustrate how you arrived at this value. B) For glucose oxidation in muscle cells, the ATP yield per CO2 formed is 6 (=36/6). What is this ratio for oxidation of i) margaric acid and ii) palmitic acid?

Explanation / Answer

17 ATP

Activation of the fatty acid to Acyl CoA = -2 ATP

Number of rounds in the Beta oxidation

(17/2) -1.5 = 8.5-1.5 = 7

7 rounds x 5 ATP/ round = 35 ATP

Number of units of Acetyl CoA produced = 7 Acetyl CoA

7 Acetyl CoA x 12 ATP/Acetyl CoA = 84 ATP

Propionyl CoA up to Succinyl CoA = -1ATP

Succinyl CoA up to Malate = 3 ATP

Malate up to Pyruvate (1 NADPH.H+)

Pyruvate up to Acetyl Co A = 3 ATP

Acetyl CoA oxidation in the Krebs Cycle = 12 ATP

Total of ATP (considering the total oxidation of Propionyl CoA converted to Malate and then from Malate to Pyruvate and then from Pyruvate to Acetyl CoA = -2 + 35 +84 -1 + 3 +3 +12 = 134 ATP

In summary (following the equivalence of 1 NADH.H+ yielding 3 ATP in the Respiratory Chain and 1 FADH2 yielding 2 ATP):

-Calculate the number of rounds of the fatty acid in the Beta-oxidation:

Number of rounds = (Number of carbons/2) -1.5

-The number of Acetyl CoA is the same as the number of rounds

-Subtract 2 ATP that were used in the initial activation of the fatty acid.

-Multiply the number of rounds x 5 ATP/round.

-Multiply the number of Acetyl CoA x 12 ATP/Acetyl CoA.

-Add 17 ATP produced in the total oxidation of Propionyl CoA to CO2

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