Saturated and unsaturated fats can undergo beta-oxidation in the mitochondrion and peroxisomes. The only major difference known so far is that peroxisomes can process linear as well as branched unsaturated fatty acid enoyl-CoA esters with much longer chains (>C20) when compared with the mitochondrion. Peroxisomal 2,4-dienoyl-CoA reductase (DECR2) mediates the reduction of long-chain enoyl-CoA esters (LCtE-CoA) to form trans-3-enoyl-CoA esters (t3enoyl-CoA) (De Nys et al. 2001, Hua et al. 2012). DECR2 functions as an auxiliary enzyme for fatty acid beta-oxidation where very long-chain and long-chain fatty acids are shortened in peroxisomes and shuttled to the mitochondrion for complete degradation.