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Fatty Acid Oxidation: Polyunsaturated Fatty Acid


β-oxidation is used to metabolize saturated fatty acyl-CoA molecules to acetyl-CoA using the 4 enzyme-catalyzed reactions shown in the scheme below. Unsaturated fatty acyl-CoA molecules, on the other hand, cannot be completely metabolized using just these 4 steps.

NEUROtiker. "File:Beta-Oxidation1.svg." Beta-oxidation. Wikimedia Commons, 7 Jan. 2007. Web. 15 June 2016. by M. Rumpho-Kennedy).

Consider the structure of the polyunsaturated fatty acid linoleic acid (${ C18:2\Delta }^{ 9,12 }$), shown in its fatty acyl-CoA form, below.

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Which of the following statements is NOT true concerning the oxidation of linoleoyl-CoA?


β-oxidation will initially proceed through 3 passes without the need for any additional enzymes and 3 acetyl-CoA will be generated.


After the original cis-${ \Delta }^{ 9 }$ bond is repositioned and converted to the trans configuration, β-oxidation can proceed directly to completion yielding a total of 9 acetyl-CoA.


After 3 passes through β-oxidation, linoleoyl-CoA is oxidized to a 12-C unsaturated fatty acyl-CoA intermediate with 2 cis double bonds at ${ \Delta }^{ 3,6 }$.


The β-oxidation enzyme enoyl-CoA hydratase cannot act on double bonds in the cis configuration.


Fatty acids with an even number of double bonds, such as seen in linoleic acid, require both an isomerase and a reductase to reposition and convert the cis double bonds to trans, in addition to the 4 enzymes of β-oxidation.