The chemical reaction that CAT catalyzes involves the amino acid histidine (Figure 6-18, in pink)which is an important part of initiating the chemical reaction (Figure 6-19):
(a) A nitrogen atom in a histidine amino acid (pink) uses some “spare electrons” to “steal” a hydrogen from the chloramphenicol. This is shown by an arrow from two red dots (electrons) “reaching out and stealing” the hydrogen from the chloramphenicol molecule (green);
(b) The electrons that previously formed the bond with the now “stolen” hydrogen, form a new bond with the carbon atom of the acetyl-CoA (blue), which is also bound in the enzyme binding pocket. This is shown by the arrow continuing to the carbon in acetyl-CoA;
(c) Step (b) causes the bond from the double carbon-oxygen in acetyl-CoA to be broken, and the electrons move to the oxygen;
(d) The electrons only stay temporarily on the oxygen and quickly move back to reform the carbon-oxygen double bond;
(e) The movement of electrons in (c) and (d) cause the carbon-sulfur bond electrons to move to the sulfur atom of the CoA molecule, ‘destroying’ the carbon-sulfur bond;
(f) The acetate group is free and separate from the “CoA”. The carbon that was previously bound to the sulfur of the CoA forms a stable covalent bond with the available oxygen on the chloramphenicol molecule.