Luminescence of a bacterial luciferase intermediate by reaction with H 2O 2: the evolutionary origin of luciferase and source of endogenous light emission

Abstract

The bacterial luciferase reaction was shown to emit light in the presence of hydrogen peroxide (H 2O 2) instead of aldehyde. Although the light intensity was weaker than that with an aldehyde, the bioluminescence emission spectrum of the luciferase reaction ( λ max 495 nm) with H 2O 2 closely agreed with that using a long chain aliphatic aldehyde (decanal). It was also found that the chemiluminescence of reduced or unreduced FMN with H 2O 2 was enhanced by peroxidase. Light emission in the luciferase reaction with H 2O 2 is attributed to a catalase-like reaction, in which the abstraction of one atom of oxygen from intermediate II (luciferase-bound FMNH-OOH) by H 2O 2 leads to the formation of excited hydroxide (E-FMNH-OH∗), H 2O and O 2. Since H 2O 2 is formed in the spontaneous breakdown of intermediate II in the absence of aldehyde, the reaction of this H 2O 2 with intermediate II can explain the origin of endogenous (non aldehyde) light emission. In the presence of luciferase, intermediate II can be formed both from FMNH 2 and oxygen, and by the reaction of H 2O 2 with FMN. The functional origin of the bacterial luciferase is postulated to be a FMN-dependent non-heme catalase which scavenges H 2O 2, concomitant with weak light emission. Prior to the association of luciferase genes ( lux AB) with the aldehyde synthesis genes ( lux CDE), forming the lux operon in luminous bacteria, the genes may have been expressed independently such that the bacteria lacked a high level of light emission.