So let's move on to step number three. Now, step number three is basically catalyzed by this methyl malnoco enzyme, a mutase. And what it does is it catalyzes an intramolecular reaction, an intramolecular rearrangement reaction in which a group, namely this entire group, is transported from the carbon number two onto this methyl group in the process that exchanges an H atom, as we'll see in just a moment. 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.