Entry M0128    photinus-luciferin 4-monooxygenase

Previous Step

Step 05

Carbon dioxide is eliminated from the intermediate with concomitant production of a photon.

GIF of Reaction Step M0128.stg05

Comment: This step occurs in the bAcs Conformation. The cleavage of the dioxetanone ring yields carbon dioxide and singlet excited oxyluciferin, which then decays emitting a photon in the green-red region of the spectrum with very high efficiency (0.88). To achieve an efficient production of singlet excited species, the breakdown of the dioxetanone ring intermediate is suggested to be activated by an intramolecular chemically initiated electron exchange luminescence (CIEEL) process. In this process, the electron transfer from the benzothiazolyl moiety of the luciferin in the phenolate form destabilizes the dioxetanone ring yielding a radical ion pair luciferin and CO2 followed by the return of the electron to generate a singlet excited state of the oxyluciferin moiety [3 6].


Electron Transfer
Intramolecular Elimination

Mechanism Components

Bond Cleavage
Bond Order Change
Intermediate Collapse
Intermediate Terminated
Overall Product Formed

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Thr343A Side Chain spectator Not Active
Thr343A Main Chain Amide spectator Not Active
Lys443 Side Chain spectator Hydrogen Bond Donor
Electrostatic Stabiliser

Metal Cofactors involved in Step 05

Metal Type Metal Identity Chain Activity Function
magnesium MG(not in PDB) 1 x spectator Not Active

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved
The C-O bond changes from a single to double bond
The C-O bond changes from a single to double bond

View similar reactions in MACiE.