Osamu Shimomura: Chemistry of Bioluminescence

Bioluminescence is common, especially in marine organisms. Shimomura classified thes into a couple of types: luciferain, photoprotein, and an undefined "other". Luciferin requires an enzymatic (luciferase) reaction, and luminescence is proportional to the concentration of the substrate. The photoprotein type requires a single molecule — aequorin, symplectin, pholasin, etc.

He summarized how D-Luciferin is converted to Oxyluciferin in the presence of O2 and ATP, catalyzed by luciferase, to produce light, either red light in acidic media or yellow green in alkaline media. There is also a variant of this reaction called coelenterazine-luciferase luminaescence, found in many marine organisms, like Periphylla, a ellyfish, and Chiroteuthis, a squid. Coelenterazine is converted to coelenteramide in the presence of O2 to produce light and CO2.

Another organism is Cyprodana, a crustacean that uses a luciferin variant — produces a very pretty blue glow.

Luminiscent bacteria convert luciferin into a fattye acid, FMN, to produce light, which is also luciferase-catalyzed. Luciferase seems to be popping up all over the place — unfortunately, Shimomura doesn't talk much at all about variations in the enzyme, but is more focused on giving us the chemical intermediates produced in the reaction. Typical chemist!

This is especially unfortunate since the luciferase reaction in different organisms seems to produce very different reaction products…it's getting me very curious about how these different forms of the protein must differ to be yielding such different outcomes, all only similar in that they also produce light as a byproduct. And then we see that some very different phyla, such as krill and dinoflagellates, use nearly identical reactions.

Photoproteins: he talks about Aequorea aequorea, which produces green light with a protein called aequorin that binds a complex molecule that resembles coelenterazine, that undergoes a conformational change in the presence of calcium ions to produce green light. If GFP is used, it produces green light.

A squid, Symplectoteuthis, converts dehydrocoelenterazine to symplectin which then produces light.

Then he switches to talking about fungal biolominescence in Mycena and Panellus, mushrooms that glow green. The precursor is decanoylpanal is conferted to luciferin, which produces light in the presence of superoxides, O2, and tetradecanoylcholine. The reaction can take place in the absence of any enzyme.

Shimomura is not exactly a dynamic speaker — he basically just read off his list of reactions — but at least he had lots of pretty pictures of glowing organisms. If only he'd said something about the relationships and evolutionary differences between them all!