Bioluminescence firefly luciferins, mechanism

Later, fireflv oxyluciferin was successfully synthesi2ed (403. 408) and has been isolated and identified in firefly lanterns (luciola cruaciata) after the lanterns were treated with pyridine and acetic anhydride to prevent decomposition (409). In 1972, Suzuki and Goto firmly established that oxyluciferin is involved in the bioluminescence of firefly lanterns and in the chemiluminescence of firefly luciferin (403. 410).. A. mechanism involving a four-membered ring cyclic peroxide has been proposed for the reaction (406. 411). However, it was not confirmed by 0 -labelinE experiments (412). 

In the postulated bioluminescence mechanism, firefly luciferin is adenylated in the presence of luciferase, ATP and Mg2+. Luciferyl adenylate in the active site of luciferase is quickly oxygenated at its tertiary carbon (position 4), forming a hydroperoxide intermediate (A). 

Fig. 1.12 Mechanism of the bioluminescence reaction of firefly luciferin catalyzed by firefly luciferase. Luciferin is probably in the dianion form when bound to luciferase. Luciferase-bound luciferin is converted into an adenylate in the presence of ATP and Mg2+, splitting off pyrophosphate (PP). The adenylate is oxygenated in the presence of oxygen (air) forming a peroxide intermediate A, which forms a dioxetanone intermediate B by splitting off AMP. The decomposition of intermediate B produces the excited state of oxyluciferin monoanion (Cl) or dianion (C2). When the energy levels of the excited states fall to the ground states, Cl and C2 emit red light (Amax 615 nm) and yellow-green light (Amax 560 nm), respectively.

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. 

Fig. 6.3.5 A reaction scheme proposed by Tsuji (2002) for the Watasenia bioluminescence. The proposed mechanism involves the adenylation of luciferase-bound luciferin by ATP, like in the bioluminescence of fireflies. However, the AMP group is split off from luciferin before the oxygenation of luciferin, differing from the mechanism of the firefly bioluminescence. Thus the role of ATP in the Watasenia bioluminescence reaction remains unclear. Reproduced with permission from Elsevier.

Bioluminescence, the phenomenon of biological light emission, has fascinated mankind for many centuries. Scientists have been intrigued by it, and for many years have tried to answer simple questions like how and why certain animals and bacteria bioluminesce. This research has led to new insights in (molecular) biology and biochemistry. For example, in the 1960s, McCapra studied the chemical mechanisms of bioluminescence and devised a model for firefly luciferin the acridan esters (Fig. 1) [1-5],... 

Of the many types of bioluminescence in nature, that of the firefly represents the most thoroughly studied and best understood biological luminescent process. The molecular mechanism of light emission by the firefly was elucidated in the 1960s in which a dioxetanone (a-peroxy lactone) was proposed as an intermediate, formed by the luciferase-catalyzed enzymatic oxidation of the firefly luciferin with molecular oxygen (Scheme 15). This biological reaction constitutes one of the most efficient luminescent processes known to date . Hence, it is not surprising that the luciferin-luciferase system finds wide use... 

McElroy, W. D., Seliger, H. H., and White, E. H. (1969) Mechanism of bioluminescence, chemiluminescence and enzyme function in the oxidation of firefly luciferin. Photochem Photobiol. 10, 153-170. 

Earlier, we found that heavy-atom effect can also be observed in bioluminescent systems 3,4 bioluminescence inhibition coefficients were found to decrease in the series potassium halides KC1, KBr, and KI. Two mechanisms can be responsible for the change of the intensity of bioiuminescence in the presence of heavy ions the physicochemical effect of external heavy atom mentioned above, and the biochemical effect, i.e. interactions with the enzymes resulting in changes in enzymatic activity. A series of model experiments was conducted to evaluate the contribution of the physicochemical mechanism. These involved the photoexcitation of model fluorescent compounds close to bioiuminescence emitters in chemical nature and fluorescent properties - flavin mononucleotide, firefly luciferin and coelenteramide. These results are clear evidence of the smaller contribution of the physicochemical mechanism to the decrease in the bioiuminescence intensity for the three bioluminescent systems under study.4... 

Firefly luciferin (111 R = R = H, X = OH) and a number of its analogues were synthesized by previously established reaction sequences from a variety of substituted 2-cyanobenzothiazoles (109) and cysteines (110). Amongst others, homoluciferin (112) and 5, 7 -dimethyl-luciferin (113) are accessible in this way. Their adenylates were produced by the condensation of the free acids with adenosine monophosphate in the presence of dicyclohexylcarbodi-imide. These were used in detailed spec-trophotometric studies of their chemiluminescence (initiated by bases), their fluorescence, and their bioluminescence under the influence of luciferase the possible mechanisms of these processes were discussed. ... 

Fig. 1.13 A mechanism of the decomposition of luciferin-4-peroxide in the firefly bioluminescence reaction proposed by DeLuca and Dempsey (1970), which involves a multiple linear bond cleavage.

Fig. 26 Mechanism of the ATP- and Mg2+-dependent firefly luciferase catalyzed bioluminescence oxidation reaction of D-luciferin (d-LH2) to oxyluciferin (oxy-L)...

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