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.