Researchers at the Federal University of Sao Carlos and the University of electro-Communications in Tokyo have been investigating the mechanism of the red light emissions from the railroad worm, the larva of the Phrixothrix hirtus beetle, with a view to ascertaining if the unusual light colour emission could be useful in imaging haemoglobin-rich tissues as in mammals, blood and muscular cells do not absorb red light, so luciferase-based techniques increasingly used to visualise processes taking place involving these cells do not work. Scientists have developed methods of cloning different luciferases, and the Brazilian/Japanese team have synthesised red light-emitting analogues of a related protein, luciferin, which has been tested using luciferases cloned from both fireflies and railroad worms. They found that larger luciferins interacted better with the railroad worm luciferase, emitting red light more efficiently.
“Railroad worm could assist with better medical imaging“
Principal investigator, Vadim Viviani, said: “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. 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 analogues. When these substances are examined with conventional luciferase that emits green, yellow or blue light, it’s impossible to see biochemical and pathological processes clearly because pigments such as haemoglobin and myoglobin absorb most of the light in these parts of the chromatic spectrum.”