Bioluminescent Systems

A bioluminescent system requires a luciferin and a luciferase, a substrate, a trigger, and sometimes an ancillary emitter. The structure of the luciferins and luciferases depend on their source in nature and this method of categorisation will be followed in the text below.  

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However, the linear bond cleavage hypothesis of the firefly bioluminescence was made invalid in 1977. It was clearly shown by Shimomura et al. (1977) that one O atom of the CO2 produced is derived from molecular oxygen, not from the solvent water, using the same 180-labeling technique as used by DeLuca and Dempsey. The result was verified by Wannlund et al. (1978). Thus it was confirmed that the firefly bioluminescence reaction involves the dioxetanone pathway. Incidentally, there is currently no known bioluminescence system that involves a splitting of CO2 by the linear bond cleavage mechanism. 

The bioluminescence systems of Phengodidae (railroad worms) and Elateroidae (click beetles) are basically identical to that of Lampyridae (fireflies), requiring firefly luciferin, ATP, Mg2+ and a luciferase for light emission. However, there seem to be some differences. Viviani and Bechara (1995) reported that the spectra of the luminescence reactions measured with the luciferases of Brazilian fireflies (6 species) shift from the yellow-green range to the red range with lowering of the pH of the medium, like in the case of the Photinus pyralis luciferase (see Section 1.1.5), whereas the spectra... 

The order Diptera (flies) contains the glow-worms Arachnocampa and Orfelia. The bioluminescence systems of dipterans do not utilize firefly luciferin in their light-emitting reactions, differing from the bioluminescence systems of coleopterans. In dipterans, it is extremely intriguing that the bioluminescence system of Arachnocampa appears different from that of Orfelia-. the former luminescence is activated by ATP, whereas the latter luminescence is stimulated by DTT but not by ATP. 

Overview. In the cultures of luminous bacteria, the bacterial cells are not luminous in their early stages of propagation. The formation of bioluminescence system is controlled by a substance called autoinducer that is produced by the cells of luminous bacteria. 

The autoinducer is a low molecular weight compound that is easily leached from the cells into the culture medium. By the propagation of bacterial cells, the concentration of the autoinducer in the medium increases. When the concentration reaches a certain threshold, the biosynthesis of bioluminescence system begins, and the bacteria become luminescent. The process is also called quorum sensing (Fuqua et al., 1994). 

Heat stability The Oplophorus luminescence system is more thermostable than several other known bioluminescence systems the most stable system presently known is that of Periphylla (Section 4.5). The luminescence of the Oplophorus system is optimum at about 40°C in reference to light intensity (Fig. 3.3.3 Shimomura et al., 1978). The quantum yield of coelenterazine is nearly constant from 0°C to 20°C, decreasing slightly while the temperature is increased up to 50°C (Fig. 3.3.3) at temperatures above 50°C, the inactivation of luciferase becomes too rapid to obtain reliable data of quantum yield. In contrast, in the bioluminescence systems of Cypridina, Latia, Chaetopterus, luminous bacteria and aequorin, the relative quantum yields decrease steeply when the temperature is raised, and become almost zero at a temperature near 40-50°C (Shimomura et al., 1978). 

The product coelenteramide is not noticeably fluorescent in aqueous solutions, but is highly fluorescent in organic solvents and also when the compound is in the hydrophobic environment of a protein. When coelenterazine is luminesced in the presence of Oplophorus luciferase, the solution after luminescence (the spent solution) is not fluorescent, presumably due to the dissociation of coelenteramide from the luciferase that provided a hydrophobic environment at the time of light emission. An analogous situation exists in the bioluminescence system of Renilla (Hori et al., 1973). 

One is the concerted decomposition of a dioxetanone structure that is proposed for the chemiluminescence and bioluminescence of both firefly luciferin (Hopkins et al., 1967 McCapra et al., 1968 Shimomura et al., 1977) and Cypridina luciferin (McCapra and Chang, 1967 Shimomura and Johnson, 1971). The other is the linear decomposition mechanism that has been proposed for the bioluminescence reaction of fireflies by DeLuca and Dempsey (1970), but not substantiated. In the case of the Oplopborus bioluminescence, investigation of the reaction pathway by 180-labeling experiments has shown that one O atom of the product CO2 derives from molecular oxygen, indicating that the dioxetanone pathway takes place in this bioluminescence system as well (Shimomura et al., 1978). It appears that the involvement of a dioxetane intermediate is quite widespread in bioluminescence. 

The enol-sulfate form (I), which is the precursor of the luciferin in the bioluminescence system of the sea pansy Renilla (Hori et al., 1972), can be readily converted into coelenterazine by acid hydrolysis. The enol-sulfate (I), dehydrocoeienterazine (D) and the coelenterazine bound by the coelenterazine-binding proteins are important storage forms for preserving unstable coelenterazine in the bodies of luminous organisms. The disulfate form of coelenterazine (not shown in Fig. 5.5) is the luciferin in the firefly squid Watasenia (Section 6.3.1). An enol-ether form of coelenterazine bound with glucopyra-nosiduronic acid has been found in the liver of the myctophid fish Diapbus elucens (Inoue et al., 1987). 

There are many kinds of bioluminescent squids. Some of them harbor luminous bacteria for their light emission (Harvey, 1952 Haneda, 1985), but all other luminous squids currently known utilize coelenterazine or its derivatives in their bioluminescence systems, and... 

Effect of pH. The light emission from most bioluminescence systems is affected by the pH of the medium, and some luciferases and photoproteins can be made inactive at certain pH ranges without resulting in permanent inactivation. For example, the luminescence of euphausiids can be quenched at pH 6, the luminescence of aequorin can be suppressed at pH 4.2-4A, and the luciferase of the decapod shrimp Oplophorus becomes inactive at about pH 4. In the case of Cypridina luminescence, however, the acidification of an extract to below pH 5 results in an irreversible inactivation of the luciferase. 

Anaerobic condition. Molecular oxygen is an essential requirement in a majority of bioluminescence systems. Thus, the light emission from those systems stops if molecular oxygen is completely eliminated. The methods for removing oxygen from biological fluids were discussed in detail by Harvey (1926b), which contains useful information on various procedures that are valuable even today. 

If a bioluminescence system is not inhibited by anaerobic conditions, the luminescence system probably does not require oxygen. In such a case, the luminescence system might require hydrogen peroxide, or it might involve an aequorin-like photoprotein that does not require oxygen for luminescence. 

Since the chemical mechanisms involved in bioluminescence are very diverse, there is no established protocol or methodology for isolating and studying new bioluminescent systems. Therefore, the most important factor in the study of the chemistry of... 

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