Within the realm of science and medicine, the terms luciferin and luciferase may have been commonplace for decades.
The root of both of these words is steeped in history, sometimes sparking suspicion. Why the name luciferin? The answer to that question and others will take some science as well as some Latin to answer.
Luciferase is an enzyme that catalyzes a light-producing biochemical reaction when it is in the presence of oxygen and a naturally occurring substrate called luciferin. Because of the light-emitting phenomenon, the luciferase-luciferin enzyme-substrate combination is the basis behind one of nature’s most common forms of bioluminescence.
Bioluminescence is the term referring to an organism’s ability to produce light based on a chemical reaction (note the emphasis on “lum” as in to illuminate). To put things in real-world context, a very familiar bioluminescent organism is the firefly.
This enzyme-substrate reaction is a biochemical reaction enabling certain organisms to produce light. The wavelength of this light, which ultimately determines light color, depends on the type of luciferin/luciferase used and the type of organism emitting it. For fireflies, the wavelength of emitted light is 560 nanometers (nm), which produces a yellow-green light color.
Figure 1. Bioluminescent organisms and the wavelength
produced (light color).
Before we dive in too deep, let’s just give a quick overview of what an enzyme is and what a substrate is.
Enzymes are proteins that catalyze, or speed up, a chemical reaction. And a substrate is what an enzyme acts upon.
A substrate binds to a specific area of an enzyme, which is called an active site. When the substrate binds to the active site, the enzyme causes the chemical bonds in the substrate to weaken, and this enables the chemical reaction.
Figure 2. Conceptual animation of a substrate binding to an enzyme’s active site.
A new product is formed as a result of this reaction, and light is also emitted. In the case of luciferase and luciferin, the resulting product of the reaction is called oxyluciferin (figure 3).
Figure 3. The luciferin luciferase reaction.
The basis behind the names luciferin and luciferase are rooted in Latin, and it all relates to the root term for light.
Light in Latin is Lux. However, with Latin, nouns, pronouns and adjectives have something called declensions. A declension is a variation of a word (noun, pronoun or adjective) based on its use.
And when any of these become plural, the variations change.
This, of course, is very different from English and Spanish. But let’s look at what this all means in terms of lux or light in Latin.
Table 1. Table of Latin declensions for the word lux.
Once you look at the chart, even if you don’t know too much about Latin (and that’s ok), you’ll start to see how the variations of the word light, when in Latin, could lead to words about light having the root luci in them.
When it comes to luciferin, the word specifically relates to bearing (ferre) light, or light bearing.
Table 2. Table of Latin conjugations for ferre (to bear, bring or carry) in participle form.
Consider a firefly whose lantern bears light, or bioluminescent plankton who produces light upon disturbance. When understanding the chemical basis for light production within bioluminescence, scientists pinpointed and named the chemicals that were truly responsible for bearing light.
Bioluminescent dinoflagellates in the ocean
Interesting animal phenomena have inspired all of humanity. The characteristic of flight in birds inspired human flight. The burrs on sticker seeds helped bring about the innovation of Velcro. Likewise, the properties of bioluminescence have inspired considerable innovation.
One of the most notable areas of research using the science of bioluminescence is cancer research.
Fortunately, no fireflies or marine organisms are injured in the process. Instead, researchers synthesize the chemicals. They are then able to use the light emission from the reaction to visualize tumors.
When it comes to developing potential drugs for cancer treatment, visualizing tumor growth or shrinkage is incredibly important.
Figure 4. Shows steady-state bioluminescence imaging. This is commonly used to monitor light emission over time. This method can be used to see changes in tumor size. Illustrated here, is a rendered example of a control mouse (top) showing an increase in tumor size over 25 days, while the mouse with treatment (bottom) shows a reduction in tumor size over a 25-day period.
The benefit of using luciferin is that it is not invasive and nontoxic to animals. You don’t have to surgically excise a tumor in order to visualize it.
This means that over the course of a given treatment, scientists can use specialized equipment that reads the light output in a targeted area to see how it changes over time. Therefore, the luciferin and luciferase enzymes work inside the model organism behind the scenes.
There are plenty of other ways in which the luciferase-luciferin system is used in research. Scientists have used this bioluminescent system to evaluate environmental toxicity, how effective a treatment is, looking at protein interactions and chains reactions, and viral research, just to name a few.
But what about in vaccines? Is luciferin or luciferase used in vaccines?
The luciferase enzyme and its substrate, luciferin, are not being used directly in vaccines (such as the flu, measles or COVID-19 vaccines). Nor are they an intermediate component of other products used in vaccines.
Consider your flashlight for a moment. In dark spaces or on dark nights, this is the tool you use to shine out so you can see select areas of your environment. It keeps you from stumbling, and helps you identify something very specific that you’re looking for.
Figure 5. Animation comparing the use of luciferin to the tool of a flashlight. In panel B, when a plant is touched, researchers can study the signaling chain of events that occur within the plant afterwards. In real-time, without sacrificing the plant, scientists see that genes throughout the plant are turned on in response to being touched. Like a flashlight (panel A), the luciferin-luciferase system helps scientists see specific things or events.
For researchers, this is exactly what the luciferin-luciferase reaction is. It’s a tool that lets them see something very specific.
In this sense, there would be no reason luciferin or luciferase would be used directly in the vaccine, or to produce components of the vaccine.
Plus, we must also add that as of right now, big equipment is needed for light visualization, and the human body is too big for light emission to penetrate, which means scientists could not see anything from people.
The enzyme and substrate, however, does let researchers study particular events when developing the vaccine. For instance, it may be used in diagnostics after testing the effectiveness of a vaccine. However, efficacy tests would be done in small cell culture studies or small animal studies.
Luciferin can also be used to observe the extent of viral infection, and to see what cells are infected (Garcia-Beltran, et. al., 2021).
While any particular vaccine patent may have references to luciferin and luciferase, the context they are used are either when citing a research paper related to its research background, or for validating aspects of the vaccine (like using that flashlight to see). The enzymes and substrates that were used for research aspects are always removed from the final production product and are never found within a vaccine.
Interesting research using luciferin
When it comes to bioluminescence within biotechnology, researchers have really innovated.
For instance, the Glowing Plant project was a crowdfunded scientific project with the goal of making plants that would light up using luciferin and luciferase.
While this might seem like a novelty, the big vision was a world in which streetlights could be replaced with glowing trees – something that would, in a way, give back to our ecosystems. Of course, we also acknowledge some conflicts this vision could cause that may not make that vision entirely practical.
Bioluminescence is also contributing to neuroscience, particularly when it comes to optogenetics. Optogenetics the process of using special light-sensitive proteins and light to enable researchers to monitor brain activity.
Typically, light for optogenetics is provided by an instrument, which is has limits during in vivo studies (within a living organism). This is where luciferin and luciferase can help. The genes for luciferase are paired with a protein called opsin to act as the light source (Berglund & Stern, 2021; Tung, Gutekunst & Gross, 2015). Currently, using bioluminescence for optogenetics is contributing to research on epilepsy and stroke, as well as other research studies.
Figure 6. Bioluminescence timeline. Click the image to see an enlarged version.
Bioluminescence has been observed for millennia. These observations have inspired mythology and folklore. But over time, especially as science became more of a methodic discipline, these observations were more deeply studied.
Initially, organisms observed to have bioluminescent qualities were cataloged. Such records go back as far as 23-79 CE by Pliny the Elder.
These early records, spanning into the Middle Ages and renaissance, were only recorded observations. There was still no scientific experimentation occurring, and that meant people only could speculate on the phenomenon.
Finally, in the 17th century, the father of modern chemistry - Robert Boyle along with Robert Hooke were the ones to discover that air (later determined to be oxygen) was one of the requirements for light production in a bioluminescent reaction.
As time went on, researchers were able to uncover more of the mechanisms behind the luciferin-luciferase reaction. And in the 20th century researcher Emil H. White from John Hopkins University isolated and synthesized the substrate.
Booms in molecular biology enabled researchers to use the relationship between luciferin and luciferase as a tool for real-time imaging of molecular events.
Not only has this become a tool for molecular researchers, but innovators are also finding ways to use the science of bioluminescence for new inventions.
To read more about the early history of luciferin and find the timeline, check out our article.
Berglund K, Stern MA, Gross RE. Bioluminescence-Optogenetics. Adv Exp Med Biol. 2021;1293:281-293. doi: 10.1007/978-981-15-8763-4_17. PMID: 33398820.
Bioimaging Center, (2015, August 11). Protocol for in vivo bioluminescence assay. Retrieved September 29, 2021, from https://bcf.technion.ac.il/wp-content/uploads/2015/10/IVIS-200-Protocol-for-in-vivo-bioluminescence-assay.pdf.
Brovko, L. (2010). Bioluminescence and fluorescence for in vivo imaging. In Bioluminescence and Fluorescence for in Vivo Imaging (pp. 1-149).
Garcia-Beltran, W. F., Lam, E. C., Astudillo, M. G., Yang, D., Miller, T. E., Feldman, J., ... & Balazs, A. B. (2021). COVID-19-neutralizing antibodies predict disease severity and survival. Cell, 184(2), 476-488.
Information for using luciferin in bioluminescent imaging ... Information for Using Luciferin in Bioluminescent Imaging. (2010, April 7). Retrieved November 8, 2021, from https://ki.mit.edu/files/ki/cfile/sbc/atwai/Luciferin%20Protocol%204-7-10.pdf.
Tung, J. K., Gutekunst, C. A., & Gross, R. E. (2015). Inhibitory luminopsins: Genetically-encoded bioluminescent opsins for versatile, scalable and hardware-independent optogenetic inhibition. Scientific reports, 5(1), 1-14.