Mutagenesis of firefly luciferase shows that cysteine residues are not required for bioluminescence activity

Conflicting reports exist in the literature as to whether sulfhydryl groups are essential for firefly luciferase activity. Inactivation of Photinus pyralis luciferase with N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and site-directed mutagenesis demonstrate that the cysteine residues are not absolutely required for activity. However, loss of P. pyralis luciferase activity is observed when any of the 4 cysteine residues is replaced with serine.