Biological Chemistry - Berezov, T. T., & Korovkin, B. F. 1998

Lipid Metabolism
Fatty Acid Oxidation
Oxidation of Unsaturated Fatty Acids

The Oxidation of Unsaturated Fatty acids generally proceeds in the same manner as that of saturated fatty acids, but with certain specific features. The double bonds in naturally occurring Unsaturated fatty acids (such as oleic and linoleic acids) possess the cis-configuration, whereas in the CoA esters of unsaturated acids—which serve as intermediates in the ß-Oxidation of Saturated fatty acids—the double bonds have the trans-configuration. Furthermore, the sequential removal of two-carbon units during The oxidation of unsaturated fatty acids up to the first double bond yields ∆^3,4-acyl-CoA rather than ∆^2,3-acyl-CoA, which is the standard intermediate in the ß-Oxidation of saturated fatty acids:

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Tissues contain an enzyme that catalyzes the shift of the double bond from the 3–4 position to the 2–3 position, while simultaneously converting its geometry from the cis- to the trans-configuration. This enzyme is designated as ∆^3,4-cis → ∆^2,3-trans-enoyl-CoA isomerase. Figure 11.3 illustrates The pathway of oleic acid ß-oxidation, highlighting the specific function of this enzyme*.