Bioluminescence has been leaving scientists in awe for a while now, as they have found some of the advantages it brings, especially in the medical field. However, mostly in the past, researchers have been looking at animals that emitted light within the yellow-green spectrum. The railroad worm, named so because of how it's light emissions form a line like that of a train carriage, becomes an exception to this as it emits both red and yellow-green light. In an issue of Scientific Reports earlier this year, researchers from the Federal University of São Carlos, Brazil report that the mechanism of how the worm emits light has the potential to improve medical imaging.
The team has worked on luciferase, which is an enzyme incorporated in the process of light emission by invertebrates. In a previous research, one of the writers, Vadim Viviani, has isolated luciferase from fireflies and discovered through observation in a test tube that the light emitted turns from green to red when exposed to an acidic medium. As this may be suggestive, scientists are still not sure of how the railroad worm naturally emits red light. The red light on the larva's head is for the larva to find its way in the dark, while the yellow lights along its side are to scare predators away.
While the researchers in Brazil worked on developing methods to clone luciferases, another team from Tokyo worked on the synthesis of equivalents of a related protein called luciferin. Viviani's colleague, Vanessa Rexende Bevilaqua tested the luciferin using luciferase clones from fireflies and railroad worms produced by the Brazilian team. The researchers have observed that larger luciferins made more interactions with luciferases from railroad worms, causing them to emit red light at higher efficiency.
"The luciferases that catalyze green and yellow light have a small cavity and therefore don't bind well to the large-structure luciferin analogs, which have very little luminescent activity," explained Viviani. "On the other hand, these large analogs interact well with luciferases that catalyze red light. We deduced from this that railroad worm luciferase has a large active site cavity capable of binding to the analogs."
The researchers suggested that the bio-inspiration be further studied for applications in medical imaging. This is particularly helpful because the blood cells and muscle cells of humans and other mammals do not absorb red light. This would later on help researchers and scientists in studying processes that take place in bone tissues or other hemoglobin-rich tissues.