Red Shift Of Emission Maximum Research Articles

Trp fluorescence reveals an activation‐dependent cation‐π interaction in the Switch II region of Gαi proteins

Crystal structures of Galpha(i) (and closely related family member Galpha(t)) reveal much of what we currently know about G protein structure, including changes which occur in Switch regions. Galpha(t) exhibits a low rate of basal (uncatalyzed) nucleotide exchange and an ordered Switch II region in the GDP-bound state, unlike Galpha(i), which exhibits higher basal exchange and a disordered Switch II region in Galpha(i)GDP structures. Using purified Galpha(i) and Galpha(t), we examined the intrinsic tryptophan fluorescence of these proteins, which reports conformational changes associated with activation and deactivation of Galpha proteins. In addition to the expected enhancement in tryptophan fluorescence intensity, activation of GalphaGDP proteins was accompanied by a modest but notable red shift in tryptophan emission maxima. We identified a cation-pi interaction between tryptophan and arginine residues in the Switch II of Galpha(i) family proteins that mediates the observed red shift in emission maxima. Furthermore, amino-terminal myristoylation of Galpha(i) resulted in a less polar environment for tryptophan residues in the GTPase domain, consistent with an interaction between the myristoylated amino terminus and the GTPase domain of Galpha proteins. These results reveal unique insights into conformational changes which occur upon activation and deactivation of G proteins in solution.

Inhibition of rice bran lipase by azadirachtin from Azadirachta indica

AbstractBACKGROUND: Chemical constituents of the neem tree are extensively explored; the major component present in the tree is azadirachtin. Azadirachtin, a tetranortriterpenoid, is remarkable for its chemical complexity and for its biological activity. This study, for the first time, has provided information on the interaction and inhibition of rice bran lipase (RBL) by azadirachtin. RBL, an esterase, is a versatile enzyme that catalyzes the hydrolysis of ester linkages, primarily in neutral lipids such as triglycerides.RESULTS: The catalytic activity of RBL in the presence of azadirachtin has been investigated. There was a decrease in enzyme activity relative to the control at all concentrations tested. At 1 mmol L−1 concentration of azadirachtin the enzyme loses 84% of its activity. The kinetics of inhibition of RBL by azadirachtin are competitive in nature. From analysis of the kinetic data the inhibition constant Ki is found to be 0.14 mmol. Fluorescence measurements showed a gradual decrease in emission intensity; a red shift in emission maximum may be attributed to perturbation of the aromatic residues. Far‐ultraviolet circular dichroism results showed minor conformational changes.CONCLUSION: The results suggest that azadirachtin specifically inhibits and binds to RBL in bringing about inhibition with minor structural alteration. This inactivation of RBL by azadirachtin can be utilized to prevent oxidation of RBL with an ultimate goal of exploiting the potential of the plant source for producing edible‐grade oil from rice bran using a natural molecule at very low concentration. Copyright © 2009 Society of Chemical Industry

Bisquinolones as chiral fluorophores – A combined experimental and computational study of absorption and emission characteristics

Biscarbostyrils (4,4′-bisquinolones) can be synthesized from 4-chloro-2-quinolinones using a Pd-catalyzed one-pot borylation/Suzuki cross-coupling protocol or via Ni(0)-mediated reductive homocoupling. The electronic spectra of biscarbostyrils 4b– 8 exhibit unusual properties in comparison to the corresponding carbostyrils 1– 3. Similar absorption spectra are accompanied by red-shifted emission maxima up to 520 nm. Unsubstituted biscarbostyril 4b displays the unusual property of a 2500 cm −1 fluorescence redshift in water as compared to dimethylsulfoxide instead of an expected 800 cm −1 blueshift. In order to further improve redshifts and fluorescence quantum yields, varying substitution patterns were created. In bisquinolone 7, an additional diphenylphosphinoxide substitution in position 3 and 3′ ( 15c) increased the quantum yield to 20% and the epsilon value to 25,000. A crown ether linkage from position 6 to 6′ in biscarbostyrils improved the emission maximum from 470 to 500 nm, but the fluorescence quantum yield was raised only from 3% to 6%. Time-dependent density functional calculations of absorption and emission spectra of selected derivatives show good agreement with the corresponding experimental data. Especially, the unusual large Stoke’s shift observed for biscarbostyrils as well as their rather low fluorescence quantum yields can be rationalized on the basis of these calculations. Like 1,1′ binaphthalenes the biscarbostyril structures are axially chiral and can be functionalized in position 3 and 3′ with diphenylphosphine. Most of the racemates were baseline HPLC separated on the Pirkle type ULMO column, with separation factors of up to 2.4 for BINAP type intermediate 15a.

Synthesis, photophysics, electrochemical and electroluminescent properties of divinylene compounds with phthalimide moieties

Three new divinylene compounds F, C and P which contained fluorene, carbazole and phenylene as central unit, respectively, and terminal phthalimide groups were synthesized by Heck coupling. The alkyl or alkoxy chains attached to the central unit as well as the cyclohexyl ring attached to the terminal phthalimides render the samples very soluble in common organic solvents. They had relatively low glass transition temperatures ( T g's), being in the range of 54–81 °C. P was stable up to about 200 °C while F and C were stable up to 300 °C. The absorption maximum was located at 387–440 nm with optical band gap of 2.48–2.56 eV. They emitted blue-green light with emission maximum at 484–562 nm. P showed the most red-shifted absorption and emission maximum. The HOMO and LUMO levels of the compounds, estimated from their cyclic voltammograms, were −6.42 to −5.58 eV and −3.06 to −2.99 eV, respectively, from which their band gaps were estimated to be 3.36 eV, 2.68 eV, and 2.52 eV. The emission spectra and performance of the EL devices, using blends of the compounds and PVK as emitting layer, also depended strongly on the compounds. The P device emitted green light (530 nm) with maximal luminance and current efficiency being at 1358 cd/m 2 and 0.57 cd/A, while those of the F device were green-blue (490 nm), 593 cd/m 2 and 0.22 cd/A.

The influence of crystal packing on the solid state fluorescence behavior of alkyloxy substituted phenyleneethynylenes

The study reports the solid state photophysical properties of a series of alkyloxy-substituted oligo(phenyleneethynylene)s, methoxy to hexyloxy, supported by a detailed analysis of molecular packing obtained from single crystal X-ray diffraction data. While the emission peaks are highly red shifted (by as much as 114 nm) in the solid state, all molecules exhibit similar absorption and emission in dilute solutions. The red shift is maximum in ethoxy and minimum in methoxy, while other crystalline films exhibit intermediate values. In the crystal structures, the spacing between the molecular pairs forming the J-aggregates is varied between 3.48 to 4.65 A, with no systematic dependence on the chain length. The red shifted emission maximum is found to vary linearly with the spacing between the interacting molecules in the J-aggregate. Thus, the emission in the solid state is determined by the extent of dipolar coupling between the molecules, the alkyl chain length influencing the properties only indirectly.

Alternating phenylenevinylene and thienylenevinylene copolymers with cyano groups: Synthesis, photophysics and photovoltaics

Two alternating conjugated copolymers TTP and TTT were synthesized by Heck coupling of 2,3-bis-(5-bromothiophene-2-yl)acrylonitrile with 1,4-dihexyloxy-2,5-divinylbenzene and 3-hexyl-2,5-divinylthiophene, respectively. The absorption spectra of the copolymers in THF solution showed three maxima around 270, 370 and 460 nm with optical band gaps of 2.30–2.34 eV. The electrochemically estimated band gaps of copolymers were 2.04–2.10 eV. The thin film absorption spectra were broad and extended about from 250 to 600 nm with a long wavelength maximum near 470 nm. The copolymers emitted yellow-orange light with maximum at 528–551 nm in THF solution and 567–610 nm in thin film. TTP showed the most red shifted emission maximum between the copolymers. The performance of the photovoltaic cells which were fabricated using blends of the copolymers with 6,6-phenyl C61-butyric acid methyl ester (PCBM) (1:1 and 1:4, w/w) as well as pure copolymers was investigated.

The Role of Intrachain and Interchain Interactions of Regioregular Poly(3-octylthiophene) Chains on the Optical Properties of a New Amphiphilic Conjugated Random Copolymer in Solution

The synthesis of a random copolymer through free radical copolymerization of a properly vinyl monofunctionalized regioregular poly(3-octylthiophene) (rrP3OT) macromonomer and N,N'-dimethylacrylamide (DMAM) is presented. The optical properties of the copolymer in water and in several organic solvents of varying polarity, as well as in THF/water and THF/methanol mixtures, were explored using UV-vis and photoluminescence spectroscopy. It is demonstrated that the rrP3OT chains adopt a coil conformation in solvents such as tetrahydrofuran (THF) and chloroform with the appearance of the absorption and emission maxima at 439 and 565 nm, respectively. On the contrary, the rrP3OT chains are organized on a single chain packing form (intrachain interactions) in polar solvents such as ethanol and methanol, as it is verified with the observation of the characteristic three vibronic features of the absorption spectra of the copolymer with maxima at 513, 550, and 603 nm and emission maxima at 560 nm. However, when water is used as solvent, the rrP3OT chains self-assemble into a stacklike structure due to the increased interchain interactions, as confirmed by the different aggregation process of the rrP3OT chains in the THF/water mixture, the broader absorption spectrum in water compared to those recorded in ethanol and methanol, and the 80 nm red-shifted emission maximum, centered at 640 nm.

Loss of structural integrity and hydrophobic ligand binding capacity of acetylated and succinylated bovine β-lactoglobulin

The lysine residues of bovine β-lactoglobulin (β-lg) were acetylated and succinylated to investigate the effect of chemical modification on tertiary and secondary structures. Both derivatives showed higher electrophoretic mobility compared with native β-lg. The molar extinction coefficients of modified proteins were lower than native β-lg. A significant decrease in intrinsic tryptophan fluorescence intensities, and a red shift of emission maxima were observed. The structural stabilities of the derivatives were compared with the native form. Both modified β-lg structures were less stable against guanidine hydrochloride and urea denaturation. Hydrophobicities decreased, as measured by hydrophobic ligand binding of the modified β-lg. Circular dichroism spectra of modified forms were different. The beta structural content of modified β-lactoglobulins decreased substantially with an increase in random coil structure. These modifications changed the tertiary structure, and involved a significant loss of secondary structure of β-lg.

Fluorescent Conjugated Polymers That Incorporate Substituted 2,1,3-Benzooxadiazole and 2,1,3-Benzothiadiazole Units

Heterocyclic monomers based on 2,1,3-benzooxadiazole and 2,1,3-benzothiadiazole bearing solubilizing side chains have been synthesized in high yields over three steps from readily available starting materials. The monomers are efficiently cross-coupled with diynes and bis(boronates) to afford high molecular weight luminescent poly(arylene ethynylene)s and polyfluorenes that exhibit red-shifted absorption and emission maxima, greater solubility, and reduced aggregation.

Synthesis and properties of the red chromophore of the green-to-red photoconvertible fluorescent protein Kaede and its analogs

Green fluorescent protein (GFP) and homologous proteins possess a unique pathway of chromophore formation based on autocatalytic modification of their own amino acid residues. Green-to-red photoconvertible fluorescent protein Kaede carries His–Tyr–Gly chromophore-forming triad. Here, we describe synthesis of Kaede red chromophore (2-[(1 E)-2-(5-imidazolyl)ethenyl]-4-( p-hydroxybenzylidene)-5-imidazolone) and its analogs that can be potentially formed by natural amino acid residues. Chromophores corresponding to the following tripeptides were obtained: His–Tyr–Gly, Trp–Tyr–Gly, Phe–Trp–Gly, Tyr–Trp–Gly, Asn–Tyr–Gly, Phe–Tyr–Gly, and Tyr–Tyr–Gly. In basic conditions they fluoresced red with relatively high quantum yield (up to 0.017 for Trp-derived compounds). The most red-shifted absorption peak at 595 nm was found for the chromophore Trp–Tyr–Gly in basic DMSO. Surprisingly, in basic DMF non-aromatic Asn-derived chromophore Asn–Tyr–Gly demonstrated the most red-shifted emission maximum at 642 nm. Thus, Asn residue may be a promising substituent, which can potentially diversify posttranslational chemistry in GFP-like proteins.

Aggregation of the hairy rod conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} in aqueous solution: an experimental and molecular modelling study

The aggregation of the fluorescent hairy rod, anionic conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) has been studied in aqueous solutions by molecular dynamics simulations, fluorescence and light scattering. Formation of clusters leads to considerable increases in light scattering, decreases in the fluorescence quantum yields and red shifts in emission maxima. Molecular dynamics simulations considering two isolated tetramers in aqueous solution show that they rapidly form aggregates, and support experimental evidence for the association of polymer chains involving both electrostatic and hydrophobic interactions. They also provide indications for proximity of aromatic rings, which is likely to be the main factor responsible for the observed fluorescence behaviour. However, there are no indications of extensive pi-stacking. The organic co-solvents methanol, acetonitrile and dioxane break up these aggregates. From studies of the dependence of the aggregation behaviour on dielectric constant or the empirical solvent parameters E(N)(T) and B(KT) for binary mixtures with water, it can be seen that this is not simply an effect of changing solvent polarity, but is due to preferential solvation of the polymer chains. This is supported by molecular dynamic simulations on two tetramers in water-dioxane mixtures (70:30%). It is suggested that similar factors are involved in both the association behaviour and aggregate disruption with other hairy rod conjugated polyelectrolytes in water.

Identification and Characterization of a New Class of Bilin Lyase: THE cpcT GENE ENCODES A BILIN LYASE RESPONSIBLE FOR ATTACHMENT OF PHYCOCYANOBILIN TO CYS-153 ON THE β-SUBUNIT OF PHYCOCYANIN IN SYNECHOCOCCUS SP. PCC 7002

Synechococcus sp. PCC 7002 and all other cyanobacteria that synthesize phycocyanin have a gene, cpcT, that is paralogous to cpeT, a gene of unknown function affecting phycoerythrin synthesis in Fremyella diplosiphon. A cpcT null mutant contains 40% less phycocyanin than wild type and produces smaller phycobilisomes with red-shifted absorbance and fluorescence emission maxima. Phycocyanin from the cpcT mutant has an absorbance maximum at 634 nm compared with 626 nm for the wild type. The phycocyanin beta-subunit from the cpcT mutant has slightly smaller apparent molecular weight on SDS-PAGE. Purified phycocyanins from the cpcT mutant and wild type were cleaved with formic acid, and the products were analyzed by SDS-PAGE. No phycocyanobilin chromophore was bound to the peptide containing Cys-153 derived from the phycocyanin beta-subunit of the cpcT mutant. Recombinant CpcT was used to perform in vitro bilin addition assays with apophycocyanin (CpcA/CpcB) and phycocyanobilin. Depending on the source of phycocyanobilin, reaction products with CpcT had absorbance maxima between 597 and 603 nm as compared with 638 nm for the control reactions, in which mesobiliverdin becomes covalently bound. After trypsin digestion and reverse phase high performance liquid chromatography, the CpcT reaction product produced one major phycocyanobilin-containing peptide. This peptide had a retention time identical to that of the tryptic peptide that includes phycocyanobilin-bound, cysteine 153 of wild-type phycocyanin. The results from characterization of the cpcT mutant as well as the in vitro biochemical assays demonstrate that CpcT is a new phycocyanobilin lyase that specifically attaches phycocyanobilin to Cys-153 of the phycocyanin beta-subunit.

A Comparative Study on Luminescent Copolymers of Fluorene and Carbazole with Conjugated or δ-Si Interrupted Structures: Steric Effects

Light-emitting alternating copolymers of 9,9-dialkylfluorene and N-hexylcarbazole with conjugated (P1 and P2) and δ-Si interrupted (P3 and P4) structures have been synthesized. The linear tetrahedral polymer P3 and hyperbranched tetrahedral polymer P4 were synthesized from two novel tetrahedral dibromo/tetrabromo precursors (2 and 3, respectively). The thermal and optical properties of all polymers in solution and the condensed state were investigated. A comparative study on the optical properties of P1−P4 showed that, in the condensed state, P1 and P2 suffered seriously from concentration quenching (significant red shift in emission maximum, broadening in emission spectrum and tremendous decrease in quantum yield), whereas the two δ-Si interrupted P3 and P4, particularly the latter, were tremendously less or not prone to self-aggregation such that they did not show significant concentration quenching in the condensed state. We represent in this paper an effective approach, a tetrahedral approach, for the synthesis of nonaggregating optoelectronic polymers.

A New Fluorescent Squaraine Probe for the Measurement of Membrane Polarity

The present study was undertaken to evaluate the sensitivity of newly synthesized squaraine dye 1 to the changes in lipid bilayer physical properties and compared it with the well-known dye 2. Partitioning of the dye 1 into lipid bilayer was found to be followed by significant increase of its fluorescence intensity and red-shift of emission maximum, while intensity of the dye 2 fluorescence increased only slightly on going from aqueous to lipidic environment. This suggests that dye 1 is more sensitive to the changes in membrane properties as compared to dye 2. Partition coefficients of the dye 1 have been determined for the model membranes composed of zwitterionic phospholipid phosphatidylcholine (PC) and its mixtures with positively charged detergent cetyltrimethylammonium bromide (CTAB), anionic phospholipid cardiolipin (CL), and sterol (Chol). The spectral responses of the dye 1 in different liposome media proved to correlate with the increase of bilayer polarity induced by Chol and CL or its decrease caused by CTAB. It was concluded that dye 1 can be used as fluorescent probe for examining membrane-related processes.

Far-red fluorescent proteins evolved from a blue chromoprotein from Actinia equina

Proteins of the GFP (green fluorescent protein) family demonstrate a great spectral and phylogenetic diversity. However, there is still an intense demand for red-shifted GFP-like proteins in both basic and applied science. To obtain GFP-like chromoproteins with red-shifted absorption, we performed a broad search in blue-coloured Anthozoa species. We revealed specimens of Actinia equina (beadlet anemone) exhibiting a bright blue circle band at the edge of the basal disc. A novel blue chromoprotein, aeCP597, with an absorption maximum at 597 nm determining the coloration of the anemone basal disk was cloned. AeCP597 carries a chromophore chemically identical with that of the well-studied DsRed (red fluorescent protein from Discosoma sp.). Thus a strong 42-nm bathochromic shift of aeCP597 absorption compared with DsRed is determined by peculiarities of chromophore environment. Site-directed and random mutagenesis of aeCP597 resulted in far-red fluorescent mutants with emission maxima at up to 663 nm. The most bright and stable mutant AQ143 possessed excitation and emission maxima at 595 and 655 nm respectively. Thus aeCP597 and its fluorescent mutants set a new record of red-shifted absorption and emission maxima among GFP-like proteins.

Water-Soluble Cationic Poly(p-phenyleneethynylene)s (PPEs): Effects of Acidity and Ionic Strength on Optical Behavior

Three cationic PPEs P1‘−P3‘ were obtained through quaternization of their neutral polymers, of which all side chains were respectively featured with a tertiary amino group (P1), an alternative tertiary amino and tri(ethylene glycol)methyl ether group (P2), and an alternative tertiary amino and dodecyloxy group (P3). P1‘ showed intrinsic water-solubility although its quaternization degree was only 45%. Slightly blue-shifted UV−vis absorption maxima in an acidic environment (maximal Δλmax ≈ 3 nm) and obvious red-shifted absorption (maximal Δλmax ≈ 30 nm) and emission maxima (maximal Δλmax ≈ 20 nm) in an alkaline environment at pH < 13 are explained in terms of pH-induced planarization of the conjugated backbone. After the pH was increased to 14, a new absorption (λmax ≈ 478 nm) and emission (λmax ≈ 495 nm) peak appeared in the redder region and the fluorescence intensity further dramatically decreased, implying the occurrence of the conformational change from the planarization of conjugated backbone to the interchain aggregation. The fluorescence enhancement of P1‘ in an acidic environment and the fluorescence decrease of P1‘ in an alkaline environment are attributed to the pH-influenced quenching ability of the nonbonding electron pair on the nitrogen atom, which belongs to the unquaternized tertiary amino group on the side chain, and the interchain aggregation. Such pH-influenced fluorescence intensity can be efficiently buffered by adding salts at pH < 10. Although adding salts in a neutral environment only creates the planarization of PPE conjugated backbone, adding salts in an alkaline environment significantly promotes the formation of interchain aggregation. Amplified quenching of P1‘ by anionic quencher Fe(CN)64- was observed and its Ksv increased significantly after adding salts or increasing pH to 14, for example from Ksv = 9.6 × 105 M-1 at pH = 7 to 7.7 × 106 M-1 at pH = 10 when [NaCl] = 0.1 M, due to the formation of elongated π-conjugation.

Carotenoid-Induced Cooperative Formation of Bacterial Photosynthetic LH1 Complex

A simple reconstitution technique has been developed and then applied to prepare a series of light-harvesting antenna 1 (LH1) complexes with a programmed carotenoid composition, not available from native photosynthetic membranes. The complexes were reconstituted with different C(40) carotenoids, having two structural parameters variable: the functional side groups and the number of conjugated C-C double bonds, systematically increasing from 9 to 13. The complexes, differing only in the type of carotenoid, bound to an otherwise identical bacteriochlorophyll-polypeptide matrix, can serve as a unique model system in which the relationship between the carotenoid character and the functioning of pigment-protein complexes can be investigated. The reconstituted LH1 complexes resemble the native antenna, isolated from wild-type Rhodospirillum rubrum, but their coloration is entirely determined by carotenoid. Along with the increase in its conjugation size, the carotenoid absorption transitions gradually shift to the red. Thus, the extension of the conjugation size of the antenna carotenoids provides a mechanism for the spectral tuning of light harvesting in the visible part of the spectrum. The carotenoids in the reconstitution system promote the LH1 formation and seem to bind and transfer the excitation energy specifically only to a species with characteristically red-shifted absorption and emission maxima, apparently, due to a cooperative effect. Monitoring the LH1 formation by steady-state absorption and fluorescence spectroscopies reveals that in the presence of carotenoids it proceeds without spectrally resolved intermediates, leading directly to B880. The effect of the carotenoid is enhanced when the pigment contains the hydroxy or methoxy side groups, implying that, in parallel to hydrophobic interactions and pi-pi stacking, other interactions are also involved in the formation and stabilization of LH1.

PH-dependent stability of EGX, a multi-functional cellulase from mollusca, Ampullaria crossean.

The cellulase activity and stability of EGX, a multi-functional cellulase previously purified from the mollusca Ampullaria crossean, was systematically studied under different pH. The pH induced con-formation and stability change of EGX have been investigated by using the intrinsic fluorescence, ANS fluorescence and CD spectrum. It has been found that the conformation and activity of this cellulase were strongly dependent on the pH. EGX was stable for both the enzyme activity and the conformation from pH 5.6 to pH 7.4. As shown by intrinsic and ANS fluorescence, no red shift of emission maximum occurred and a negligible intensity change was observed at pH 5.6-7.4. The activity of EGX remained about 80% in pH 5.6-7.4 and obviously decreased out of side the pH range. Urea-induced changes in EGX at pH 5.4 and pH 8.0 were measured by intrinsic fluorescence and CD spectrum. At pH 5.4, a significantly red shift of emission maximum occurred when the concentration of urea was 5 M compared to the concentration was 3 M at pH 8.0. The alpha-helix at pH 5.4 was 40.51% in the absence of urea and 31.04% in the presence of 4 M urea. At pH 8.0 the alpha-helix was 7.23% in the presence of 4 M urea. The data indicated that EGX was much susceptible to urea-induced unfolding at pH 8.0 and much stable at pH 5.4. The greater pH dependent stability of EGX may allow the enzyme to adequately catalyze the hydrolysis of cellulosic materials under natural or industrial extreme conditions.

An Exceptional Red Shift of Emission Maxima upon Fluorine Substitution.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionAn Exceptional Red Shift of Emission Maxima upon Fluorine Substitution.F. C. Krebs and H. SpanggaardCite this: J. Org. Chem. 2004, 69, 10, 3602Publication Date (Web):April 20, 2004Publication History Published online20 April 2004Published inissue 1 May 2004https://doi.org/10.1021/jo049476hCopyright © 2004 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views410Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (19 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Fluorescence Spectroscopic Studies on Ovis Lactoperoxidase

Ovis lactoperoxidase (sLP), on excitation at 280 nm shows fluorescence emission of a single broad maximum at 332 nm. The conformational stability was measured by unfolding studies in urea and guanidine hydrochloride. The fluorescence intensity gradually decreased with increase in urea concentrations. The decline might have been caused by partial unfolding, affecting some of the tryptophan residues. In 5 M GuHCl concentrations, a red shift in emission maximum to 356 nm was observed. It indicates that tryptophan is buried in the interior of the hydrophobic environment in native folded state and inaccessible to solvent water but on unfolding all get exposed to aqueous environment. Acrylamide is an efficient quencher and the quenching process is essentially homogenous with all tryptophan being accessible. A little quenching is observed for KI is interpreted as sLP has tryptophan residues that are buried inside the core of the protein.