This is the equation for the reaction of penicillin with a side chain amine group, –NH₂, on a protein molecule. The bond between the nitrogen and the carbonyl carbon atom of the ß-lactam ring is broken, and this carbon forms an amide, –CONH–, linkage with the amine group on the protein. At the same time, one of the protein’s amine hydrogen atoms is transferred to the N atom that was in the ß-lactam ring. The reaction results in deactivation of the protein.