Despite its name of biblical reminiscences, which invites us to think of some kind of malignant entity, luciferase is a biological compound present in bioluminescent living beings capable of emitting light, and the main responsible for this process. As in the case of the fallen angel —whose nomenclature actually dates from the 8th century—, its name comes from the Latin lux , “light”, and ferre , “to carry”, that is, “bearer of light” , with the ending ‘-ase’, a suffix indicating that it is an enzyme .
The light-carrying enzyme
Enzymes are a type of biomolecules, specifically proteins, whose function in the cell is to facilitate or carry out certain chemical reactions. Thus, they are a kind of biological catalysts , synthesized by the cells of living beings, which are responsible for carrying out metabolism. Practically all of the chemical reactions that take place inside a cell are mediated by enzymes; which are in charge of the process of respiration or digestion, intervene in the synthesis of DNA, and in the rest of metabolic processes.
Bioluminescence , as a metabolic process, has evolved independently in various groups of living beings: bacteria, fungi, algae, and many different animals. The bioluminescence process has a basic foundation: a substrate, generically called “ luciferin ”, is oxidized by the action of an enzyme, luciferase, and light is emitted as a consequence of the resulting chemical reaction.
However, as bioluminescence has emerged independently in many groups of living beings, not all use the same molecules to carry out the process. The luciferin of a firefly is completely different from that of a jellyfish, a fluorescent fungus or an abyssal fish. And if the substrate is different, the enzyme must also be different. Luciferases are, therefore, different proteins in each group of living beings.
Luciferase in the laboratory
Luciferases are enzymes with great utility in the laboratory . After all, if a luciferase has oxygen, energy and the right luciferin substrate, the result will be the emission of light, more or less dim, that can be observed with the naked eye and even measured with an apparatus. It is enough to transfer the gene that codes for the synthesis of a luciferase to a living being, to endow it with bioluminescence. Thus, we have obtained bioluminescent plants, worms and even mice . But this process is not done on a whim; There is an important purpose to giving a mouse the ability to glow in the dark.
There are multiple applications for luciferase. For example, when in biomedicine a transgenic animal is produced that contains a human gene that expresses a certain protein or is linked to a pathology, we can introduce the luciferase gene adjacently. In this way, the cells that express the introduced gene will also express luciferase, will glow in the dark and will be possible to identify them with the naked eye.
This fluorescence can also be performed in vivo and check in real time the evolution of certain types of cancer or the efficacy of certain drugs , observe how the cells of the immune system move and where they focus, or check the efficiency of gene transfer in alive .
Choosing the right luciferase
Depending on the type of study to be carried out, there will be some luciferases or others that are more interesting. Each has its own light emission spectrum, and living tissue usually absorbs some of the emitted light. For example, hemoglobin absorbs blue or green light very effectively, but red light very poorly; a problem that we would not find with the dermis or the epidermis, so selecting the appropriate enzyme may be essential for the correct performance of the study. The most widely used luciferase to date is that extracted from the firefly Photinus pyralis .
Furthermore, especially if it is to be used in living organisms, the substrate used for the luciferase reaction must be “harmless” and be well distributed throughout the tissues. In research, this substrate is often injected, and the luminescent reaction may take several minutes to manifest.
Among the limitations of these applications we find the requirement of oxygen; Most luciferases work by oxidizing the substrate luciferin, thus requiring oxygen for the reaction to take place. An exception to this generality are some jellyfish, which present a prior activation phase of luciferin, in the presence of oxygen —forming peroxyluciferin—, and the luciferase reaction can occur at another time, even in anoxic conditions.
References:
Contag, C. H. et al. 2002. Advances in In Vivo Bioluminescence Imaging of Gene Expression. Annual Review of Biomedical Engineering, 4(1), 235-260. DOI: 10.1146/annurev.bioeng.4.111901.093336
Gould, S. J. et al. 1988. Firefly luciferase as a tool in molecular and cell biology. Analytical Biochemistry, 175(1), 5-13. DOI: 10.1016/0003-2697(88)90353-3
Hastings, J. W. 1996. Chemistries and colors of bioluminescent reactions: a review. Gene, 173(1), 5-11. DOI: 10.1016/0378-1119(95)00676-1
