Luciferins, bioluminescent substances

Chemical Mechanism of Fireworm Bioluminescence - A Theoretical Proposition

Odontosyllis undecimdonta is a marine worm, commonly known as a fireworm, that exhibits bluish-green bioluminescence (BL). The luciferin (L) and oxyluciferin (OL) during fireworm BL have been experimentally identified in vitro. The L and OL are the respective starting point and ending point of a series of complicated chemical reactions in the BL. However, the chemical mechanism of the fireworm BL remains largely unknown. Before the experiments provided strong evidence for the mechanism, based on our previously successful studies on several bioluminescent systems, we theoretically proposed the chemical mechanism of the fireworm BL in this article. By means of the spin-flip and time-dependent density functional calculations, we clearly described the complete process from L to OL: under the catalysis of luciferase, L undergoes deprotonation and reacts with 3O2 to form a dioxetanone anion via the single-electron transfer mechanism; the dioxetanone anion decomposes into the OL at the first singlet excited state (S1) by the gradually reversible charge-transfer-induced luminescence mechanism; and the S1-OL emits light and deexcites to OL in the ground state.

Vascular architecture in the bacteriogenic light organ of Euprymna tasmanica (Cephalopoda: Sepiolidae)

Symbiosis between southern dumpling squid, Euprymna tasmanica (Cephalopoda: Sepiolidae), and its luminescent symbiont, the bacterium Vibrio fischeri, provides an experimentally tractable system to examine interactions between the eukaryotic host and its bacterial partner. Luminescence emitted by the symbiotic bacteria provides light for the squid in a behavior termed "counter-illumination," which allows the squid to mask its shadow amidst downwelling moonlight. Although this association is beneficial, light generated from the bacteria requires large quantities of oxygen to maintain this energy-consuming reaction. Therefore, we examined the vascular network within the light organ of juveniles of E. tasmanica with and without V. fischeri. Vessel type, diameter, and location of vessels were measured. Although differences between symbiotic and aposymbiotic squid demonstrated that the presence of V. fischeri does not significantly influence the extent of vascular branching at early stages of symbiotic development, these finding do provide an atlas of blood vessel distribution in the organ. Thus, these results provide a framework to understand how beneficial bacteria influence the development of a eukaryotic closed vascular network and provide insight to the evolutionary developmental dynamics that form during mutualistic interactions.

Simple and ultrastable all-inclusive pullulan tablets for challenging bioassays

Many biodetection systems employ labile enzymes and substrates that need special care, making it hard to routinely use them for point-of-care or field applications. In this work we provide a simple solution to this challenging problem through the creation of all-inclusive pullulan assay tablets. The proposed tablet system not only enhances the long-term stability of both enzymes and organic substrates, but also simplifies the assay procedure. The enhanced stability is attributed to two factors: the restriction of the molecular motion of proteins and impermeability to molecular oxygen afforded by the tables. These tablets dissolve rapidly upon addition to testing samples, making the test very easy to perform. Using the ATP-detecting luciferase-luciferin system as an example, we show that the tablet-based assay can achieve highly sensitive detection of ATP in biological samples and that the activity of the assay tablets remains unchanged for over a month at room temperature.

DNA Triplexes That Bind Several Cofactor Molecules

Cofactors are critical for energy-consuming processes in the cell. Harnessing such processes for practical applications requires control over the concentration of cofactors. We have recently shown that DNA triplex motifs with a designed binding site can be used to capture and release nucleotides with low micromolar dissociation constants. In order to increase the storage capacity of such triplex motifs, we have explored the limits of ligand binding through designed cavities in the oligopurine tract. Oligonucleotides with up to six non-nucleotide bridges between purines were synthesized and their ability to bind ATP, cAMP or FAD was measured. Triplex motifs with several single-nucleotide binding sites were found to bind purines more tightly than triplexes with one large binding site. The optimized triplex consists of 59 residues and four C3-bridges. It can bind up to four equivalents of ligand with apparent Kd values of 52 µM for ATP, 9 µM for FAD, and 2 µM for cAMP. An immobilized version fuels bioluminescence via release of ATP at body temperature. These results show that motifs for high-density capture, storage and release of energy-rich biomolecules can be constructed from synthetic DNA.

Firefly luciferase produces hydrogen peroxide as a coproduct in dehydroluciferyl adenylate formation

Firefly luciferase catalyzes the synthesis of H2O2 from the same substrates as the bioluminescence reaction: ATP and luciferin (D-LH2). About 80% of the enzyme-bound intermediate D-luciferyl adenylate (D-LH2-AMP) is oxidized into oxyluciferin, and a photon is emitted during this reaction. The enzyme pathway responsible for the generation of H2O2 is a side reaction in which D-LH2-AMP is oxidized into dehydroluciferyl adenylate (L-AMP). Like the bioluminescence reaction, the luciferase-catalyzed synthesis of H2O2 and L-AMP is a stereospecific process, involving only the natural D enantiomer. However, the intramolecular electron transfer postulated as essential to the light emission process is not involved in this side reaction.

Mechanistic insights in charge-transfer-induced luminescence of 1,2-dioxetanones with a substituent of low oxidation potential

We have investigated the decomposition pathway of dioxetanones 1c with a phenoxide anion group by the B3LYP/6-31+G(d) method together with the second-order multireference Møller-Plesset perturbation (MRMP) theory and propose charge-transfer-induced luminescence (CTIL) with polarization-induced branching excitation processes. In the gas phase, the thermal decomposition of 1c occurs by an asynchronous two-stage pathway without a discrete intermediate; that is, the initial O-O bond breaking to generate a charge-transfer (CT) diradical species is immediately followed by the subsequent C-C bond breaking with simultaneous back CT, which is responsible for the surface crossing at the avoided crossing. The activation energy is dramatically reduced from 19.4 to 3.8 kcal mol(-)(1) by the deprotonation of phenol meta-1d to its anion meta-1c, showing an important role of the endothermic CT. The odd/even selection rule for the chemiluminescence efficiency can be explained by the orbital interaction for the back CT between the carbonyl pi orbital and either a HOMO or a LUMO of the generated light emitters. To examine the accessibility of the chemically initiated electron exchange luminescence (CIEEL) route, we considered the solvent effects on the free-energy change of meta-1c by using continuum solvent models. The bending vibration mode of the CO(2) fragment is specifically considered. Borderline features emerges from the solution-phase CT reaction of meta-1c, which depends on the solvent polarity: one is a nonadiabatic or adiabatic back CT process (polarization-induced concerted CTIL), and the other is a radical dissociation, i.e., complete one-electron-transfer process (CIEEL).

A Likely Biogenetic Gateway Linking 2-Aminoimidazolinone Metabolites of Sponges to Proline: Spontaneous Oxidative Conversion of the Pyrrole-Proline-Guanidine Pseudo-peptide to Dispacamide A

A new spontaneous oxidative transformation of the associated pyrrole-proline-guanidine to the natural marine pyrrole 2-aminoimidazolinone derivative has been achieved. The sensitive reaction requires air oxygen and the N-acylation of proline by pyrrole-2-carboxylic acid. Proline metabolism and pyrrole 2-aminoimidazole secondary metabolites formation seem to be related and are utilized by sponges under stress conditions for their defense against predators. A plausible stress-induced oxidative chemical pathway that establishes dispacamide derivatives as the forerunners in the biogenetic synthesis of the key pyrrole 2-aminoimidazole oroidin is proposed. The mechanism of the reaction seems to be another development of the known luciferins' chemiluminescent reactions in bioluminescent marine organisms.

Separation, identification and determination of luciferin in the Iranian firefly, Lampyris turkestanicus by HPLC and spectroscopic methods

Iranian firefly larvae, Lampyris turkestanicus collected from north of Iran and their luciferin were analyzed by HPLC, TLC, MS and spectroscopic Fourier transform ([FT]-IR, FT-NMR, UV and fluorescence) methods. The results showed that luciferin in L turkestanicus lanterns was the same as in the American firefly, Photinus pyralis and synthetic D-luciferin.

Shining the light: the mechanism of the bioluminescence reaction of calcium-binding photoproteins

The Ca2+-binding photoproteins from jellyfish have the unique ability to emit blue light in the presence of calcium ions but without molecular oxygen or any other cofactor. Although there is no crystallographic data on the structure of the photoprotein complex, structure-activity studies have elucidated many features of the complex and many aspects of the mechanism of the bioluminescence reaction.