"The luciferases of the Phrixotrix railroad worms are the only [OLE2] luciferases that naturally catalyse bioluminescence in the red region of the spectrum…Despite the similarity of their primary sequences, the Phrixotrix luciferases display remarkably different physicochemical properties. The active site of the red-emitting PxRE luciferase displays substrate affinities, catalytic efficiency, and a dielectric constant higher than those of the PxGR luciferase. These results suggest that the benzothiazolyl side of the luciferin-binding site of PxRE luciferase is tighter and more polar than that of PxGR luciferase. Mutagenesis studies suggest that differences in the thiazolyl portion of the luciferin binding site, during the emitting step, could be responsible for differences of bioluminescence colors in these luciferases." (Viviani et al. 2006:467, 473)
Active-site properties of Phrixotrix railroad worm green and red bioluminescence-eliciting luciferases
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