Now, just like in the case of this carboxylase, it requires biotin for its activity. In the case of this mutase, it requires vitamin B twelve. In fact, with that vitamin B twelve, this reaction would not actually take place. So let's see exactly what we mean by an intramolecular rearrangement reaction that is catalyzed by this mutase. And let's begin with this l isomer of methylmalcouncilma that we formed in step number two. So this is our molecule.