Solvent and pH dependence of fluorescence spectra of 9-phenanthrylamine

1983 ◽  
Vol 61 (6) ◽  
pp. 1064-1066 ◽  
Author(s):  
Meenakshisunderam Swaminathan ◽  
Sneh Kumar Dogra
Keyword(s):  
Fluorescence Spectra ◽  
Ph Dependence ◽  
Neutral Form ◽  
Unusual Behaviour ◽  
Proton Concentration

Fluorimetric titrations were carried out for various forms of 9-phenanthrylaminc and pKa* values were determined. An unusual behaviour observed in the fluorimetrie titration of the neutral form at moderate proton concentration is due to the quenching of the S1 state of PNH2 by H+.

scholarly journals Quinoxalinedione deprotonation is important for glutamate receptor binding

2019 ◽  
Vol 400 (7) ◽  
pp. 927-938 ◽  
Author(s):  
Adela Dudić ◽  
Andreas Reiner
Keyword(s):  
Ph Dependence ◽  
Binding Pocket ◽  
Ionotropic Glutamate Receptors ◽  
Kainate Receptor ◽  
Binding Assays ◽  
Neutral Form ◽  
Glutamate Binding ◽  
Binding Data ◽  
Electrostatic Contribution

Abstract Quinoxalinediones are an important class of competitive antagonists at ionotropic glutamate receptors (iGluRs), where they are widely used to block α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptor responses. In this study we utilize two prototypic quinoxalinedione antagonists, namely DNQX and CNQX, which quench the intrinsic fluorescence of the ligand binding domain (LBD), to perform in vitro binding assays. We find that binding of DNQX and CNQX at the AMPA receptor GluA2 LBD is strongly pH dependent, whereas glutamate binding is not affected by pH. We also show that the deprotonation of DNQX, CNQX and other quinoxalinediones (NBQX and YM90K) occurs close to physiological pH, which can be explained by the lactam-lactim tautomerization of the quinoxalinedione scaffold. Analysis of our binding data indicates that quinoxalinedione deprotonation is a key requirement for binding, as we find a >100-fold higher affinity for binding of the monoanionic form compared to the neutral form. This suggests a large electrostatic contribution to the interaction with a conserved arginine residue located in the binding pocket of iGluRs. The strong pH dependence of quinoxalinedione binding, which has not previously been reported, is relevant for structure-function studies, but also for the use of quinoxalinediones in physiological experiments and envisioned therapeutic applications.

scholarly journals Mismatch dependent uracil/thymine-DNA glycosylases excise exocyclic hydroxyethano and hydroxypropano cytosine adducts.

2005 ◽  
Vol 52 (1) ◽  
pp. 149-165 ◽  
Author(s):  
Ewa Borys-Brzywczy ◽  
Katarzyna D Arczewska ◽  
Murat Saparbaev ◽  
Ulrike Hardeland ◽  
Primo Schär ◽  
...  
Keyword(s):  
Ph Dependence ◽  
Protonated Form ◽  
Dna Bases ◽  
Dna Glycosylases ◽  
Neutral Form ◽  
Hydrogen Bond Interaction ◽  
Strong Base ◽  
Human Enzyme ◽  
Ph Range ◽  
Exocyclic Adducts

Exocyclic adducts of DNA bases, such as etheno- and hydroxyalkano- ones, are generated by a variety of bifunctional agents, including endogenously formed products of lipid peroxidation. In this work we selectively modified cytosines in the 5'-d(TTT TTT CTT TTT CTT TTT CTT TTT T)-3' oligonucleotide using: chloroacetaldehyde to obtain 3,N(4)-alpha-hydroxyethano- (HEC) and 3,N(4)-etheno- (epsilonC), acrolein to obtain 3,N(4)-alpha-hydroxypropano- (HPC) and crotonaldehyde to obtain 3,N(4)-alpha-hydroxy-gamma-methylpropano- (mHPC) adducts of cytosine. The studied adducts are alkali-labile which results in oligonucleotide strain breaks at the sites of modification upon strong base treatment. The oligonucleotides carrying adducted cytosines were studied as substrates of Escherichia coli Mug, human TDG and fission yeast Thp1p glycosylases. All the adducts studied are excised by bacterial Mug although with various efficiency: epsilonC >HEC >HPC >mHPC. The yeast enzyme excises efficiently epsilonC>HEC>HPC, whereas the human enzyme excises only epsilonC. The pH-dependence curves of excision of eC, HEC and HPC by Mug are bell shaped and the most efficient excision of adducts occurs within the pH range of 8.6-9.6. The observed increase of excision of HEC and HPC above pH 7.2 can be explained by deprotonation of these adducts, which are high pK(a) compounds and exist in a protonated form at neutrality. On the other hand, since epsilonC is in a neutral form in the pH range studied, we postulate an involvement of an additional catalytic factor. We hypothesize that the enzyme structure undergoes a pH-induced rearrangement allowing the participation of Lys68 of Mug in catalysis via a hydrogen bond interaction of its epsilon-amino group with N(4) of the cytosine exocyclic adducts.

scholarly journals A kinetic and fluorimetric investigation of papain modified at tryptophan -69 and -177 by N–bromosuccinimide

1974 ◽  
Vol 141 (2) ◽  
pp. 503-515 ◽  
Author(s):  
Gordon Lowe ◽  
Alan S. Whitworth
Keyword(s):  
Fluorescence Intensity ◽  
Fluorescence Spectra ◽  
Close Contact ◽  
Ph Dependence ◽  
Thiol Group ◽  
Structural Features ◽  
Enzymic Activity ◽  
Ph Profile ◽  
Hydrolysis Of ◽  
Nitrophenyl Ester

A systematic study of the modification of papain (its thiol group protected as a disulphide with mercaptoethanol) by N-bromosuccinimide, showed that 2 molar equiv. modified tryptophan-69 and 4 molar equiv. modified tryptophan -69 and -177. The Michaelis parameters for the catalysed hydrolysis of N-benzyloxycarbonylglycine p-nitrophenyl ester by these modified enzymes were determined. The enzymic activity of the modified enzymes was not seriously impaired, but modification of tryptophan-177 raised the apparent pKa of the acidic limb of the pH profile by more than 1 pH unit for both kcat. and kcat./Km. The fluorescence spectra (excitation at 288nm) of the modified enzymes showed that tryptophan -69 contributed about 8% to the fluorescence intensity, whereas tryptophan-177 contributed about 46% at neutral pH. However, the contribution of tryptophan -177 was quenched at low pH and its fluorescence intensity showed sigmoidal pH-dependence, with an apparent pKa of 4.2. Histidine -159, which is in close contact with tryptophan -177, is considered to be the residue responsible for the fluorescence quenching. When tryptophan -177 was modified, presumably generating a less hydrophobic micro-environment, the apparent pKa determined kinetically was raised to about 5.4. By comparing the Michaelis parameters of native papain, papain modified at tryptophan-69 and papain modified at tryptophan-69 and -177 with N–benzyloxycarbonylglycylglycine amide and N–benzyloxycarbonylglycyltryptophan amide, tryptophan-69 and tryptophan -177 were shown to be structural features of the S2 and S1′ subsites respectively.

Raman And Fluorescence Spectra Observed in Laser Microprobe Measurements of Several Compositions in the Ln-Ba-Cu-O System

1990 ◽  
Vol 48 (2) ◽  
pp. 278-279
Author(s):  
Edgar S. Etz ◽  
Thomas D. Schroeder ◽  
Winnie Wong-Ng
Keyword(s):  
Fluorescence Spectra ◽  
Single Phase ◽  
X Ray Diffraction ◽  
Ceramic Powders ◽  
Conventional Solid State Reaction ◽  
X Ray ◽  
Raman Microprobe ◽  
Methods Of Synthesis ◽  
Compositional Homogeneity ◽  
Processing Techniques

We are investigating by Raman microprobe measurements the superconducting and related phases in the LnBa2Cu3O7-x (for x=0 to 1) system where yttrium has been replaced by several of the lanthanide (Ln = Nd,Sm,Eu,Ho,Er) elements. The aim is to relate the observed optical spectra (Raman and fluorescence) to the compositional and structural properties of these solids as part of comprehensive materials characterization. The results are correlated with the methods of synthesis, the processing techniques of these materials, and their superconducting properties. Of relevance is the substitutional chemistry of these isostructural systems, the differences in the spectra, and their microanalytical usefulness for the detection of impurity phases, and the assessment of compositional homogeneity. The Raman spectra of most of these compounds are well understood from accounts in the literature.The materials examined here are mostly ceramic powders prepared by conventional solid state reaction techniques. The bulk samples are of nominally single-phase composition as determined by x-ray diffraction.

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