Unsaturated fatty acids require some additional processing before they can be degraded completely by β-oxidation. The Unsaturated fatty acyl CoAs with double bonds at odd-numbered carbon atoms example between, for instance, C-9 and C-10 as in palmitoleate are acted on in the common way by the degradation mechanism unless the acyl CoA dehydrogenase encounters the cis- Δ3-enoyl CoA created at the end of the third round. The presence of the double bond between C-3 and C-4 avoids the formation of another double bond between C-2 and C-3. To overcome this problem an isomerase converts the cis- Δ3 bond into a trans-Δ2 twice bond, and the resulting trans-Δ2-enoyl CoA can then regularly down the β-oxidation pathway.