Source of oxygen in the CO 2 produced in the bioluminescent oxidation of firefly luciferin

Incorporation of (18)O into the CO(2) produced in the bioluminescent oxidation of firefly luciferin was studied. In H(2) (16)O medium with (18)O(2) gas, the product CO(2) contained up to 75% C(16)O(18)O, showing that one O of the product CO(2) arose from the O(2) that oxidized luciferin. This result is consistent with a dioxetane mechanism. Analysis of the mass spectral data of the CO(2) obtained in high-enrichment H(2) (18)O medium with (16)O(2) gas indicated the presence of about 20% contaminating CO(2), which contributes approximately 70% of the total incorporated (18)O. Thus the values of incorporated (18)O in H(2) (18)O medium with (16)O(2) gas have no significance in the present context. Data obtained with luciferases of the American firefly Photinus and Japanese firefly Luciola were similar.