The enzyme malonyl-CoA decarboxylase (MCD) functions as an indirect via of conversion from malonic semi aldehyde to acetyl-CoA in peroxisomes. This is due to the fact that the beta oxidation of long chain fatty acids with an odd number of carbons produces propionyl-CoA. Most part of this metabolite is transformed into succinyl-CoA, which is an intermediate of the tricarboxylic acid cycle. The major alternative route by which the propionyl-CoA is metabolized is based on its conversion to acrylyl-CoA. After that, it is converted to 3-hydroxy propionic acid and finally to malonic semi-aldehyde. As soon as malonic semi aldehyde is produced, it is indirectly transformed into acetyl-CoA. This conversion has been detected only in bacteria, in the other natural kingdoms there is no scientific evidence to prove it.