This is what I'd like to focus on in this lecture. And let's begin with step number one. In step number one, we basically want to transform this three carbon molecule, the proponental coenzyme A, into a four carbon molecule known as demethylmel coenzyme A. And the enzyme that catalyzed this reaction is a carboxylase. Now, anticurboxylase requires three things. It needs an energy source, it needs a carbon source, and it needs vitamin B molecule.