So we can now build antibodies with specific catalytic capabilities by using transition state analogues as antigens. And to demonstrate how this actually works, let's discuss the biosynthesis process, the biosynthesis of the heme groups. So remember, in proteins such as hemoglobin and myoglobin, we have these important prosthetic groups known as heme groups. And at the center of the heme group is the protiporphine ring. So the protoporphine ring basically is that organic part of that heme group that actually carries, that holds that iron atom. Now, in the process of the synthesis of this protoporphine ring, of the hemegroup, the final step is to basically use a special enzyme known as ferrokeletase to basically catalyze the insertion of that se atom, the metal atom, into the center of the protiporphine ring.