BIOLUMINESCENCE OF BRAZILIAN FIREFLIES (COLEOPTERA: LAMPYRIDAE): SPECTRAL DISTRIBUTION and pH EFFECT ON LUCIFERASE‐ELICITED COLORS. COMPARISON WITH ELATERID and PHENGODID LUCIFERASES

Abstract— Twenty‐five Brazilian species (nine genera: Phorinus, Photinoides, Macrolampis, Aspisoma, Cratomorphus, Amydetes, Photuris, Bicellonychia, Pyrogaster) of adult fireflies were found to emit light in vivo in the green‐yellow range (Λ max =548–573 nm) of the spectrum, more frequently near the green region, in contrast with North‐American species, which predominantly emit yellow light. Distinct ecological contexts where these species evolved, such as the habitat (open field vs forests) and the duration of twilight, are discussed as possible factors responsible for these differences. Except for Photuris and Bicellonychia spp., the in vivo and in vitro bioluminescence spectra for various species of a given genus agree within ±5 nm. Lowering the pH caused the typical red shift in the in vitro bioluminescence spectrum from lampyrid luciferases (six species), which has been interpreted as due to the presence of a basic residue in the enzyme active site catalyzing fast enolization of the initially formed excited keto‐oxyluciferin (red emitter) to the excited enol form (yellow‐green emitter). The in vitro bioluminescence colors obtained from larval or adult elaterid (five species) and phengodid (three species) luciferases studied here, spanning the green‐red region, do not respond to pH changes. This could indicate either the absence of the neighboring basic center (in red‐emitting luciferases) or the presence of a non‐pH affected proximal basic residue in the active site of the luciferase (in yellow‐green‐emitting luciferases).