Purification of the yellow fluorescent protein from vibrio fischeri and identity of the flavin chromophore

A low molecular weight protein (~ 25,000 D) exhibiting a yellow fluorescence emission peaking at ~ 540 nm was isolated from Vibrio fischeri (strain Y-1) and purified to apparent homogeneity. FMN is the chromophore, but it exhibits marked red shifts in both the absorption (λmax = 380, 460 nm) and the fluorescence emission. When added to purified luciferase from the same strain, which itself catalyzes an emission of blue-green light (λmax ~ 495 nm), this protein induces a bright yellow luminescence (λmax ~ 540 nm); this corresponds to the emission of the Y-1 strain in vivo. This yellow bioluminescence emission is thus ascribed to the interaction of these two proteins, and to the excitation of the singlet FMN bound to this fluorescent protein