Showing papers on "Circular dichroism published in 1972"
1,853 citations
TL;DR: The experiments show that an isomerization of DNA with a certain base sequence is possible in solution and the proposed model suggests a plausible mechanism.
1,035 citations
TL;DR: It is shown that ordered binding can occur between the agarose or carrageenan helix and parts of the galactomannan backbone that contain contiguous unsubstituted mannose residues, suggesting that the binding might mimic biological cohesion between skeletal and gel phases of natural cell walls.
268 citations
TL;DR: The results strengthen the previous assignment of the CD spectrum of an unordered chain, and indicate that three conformational states (α‐helix, extended helix, and unordered) should be incorporated in the thinking about conformational transitions in polypeptides.
Abstract: The circular dichroism (CD) spectra of poly-L-proline and of poly-L-glutamic acid and poly-L-lysine in their charged states have been studied as a function of temperature. The variation of CD spectra with temperature is inconsistent with the assignment of the spectrum of such charged polypetides to an unordered chain conformation, but does support our earlier assignment to a locally ordered structure—what we have called the extended helix conformation. These results also strengthen our previous assignment of the CD spectrum of an unordered chain, and indicate that three conformational states (α-helix, extended helix, and unordered) should be incorporated in our thinking about conformational transitions in polypeptides.
212 citations
TL;DR: The molecular weight of epidermal growth factor is estimated to be approximately 6100 by the methods of sedimentation equilibrium, gel filtration, and minimum molecular weight calculations from amino acid analyses.
208 citations
TL;DR: Evidence for solvent-dependent structural changes in the Pro-Aib sequence in both cyclic and acyclic peptides is presented and generalrelations between CD spectral type and specific 0-turn conformations may not be obtained.
Abstract: Nuclear Overhauser effects (NOE) and circular dichroism (CD) techniques have been used to probe @-turn conformations
in acyclic and cyclic peptides containingPro-Xsequences. The model peptides studied are of the type Piv-Pro-X-NHMe (X
= Aib, D-Ala, Gly, Val, and Leu) and Boc-Cys-Pro-X-C s NHMe (X = Aib, L-Ala, D-Ala, Gly, and Leu). In the acyclic series, observation of NOES between Pro C"H and X-NH, together with solvent and temperature dependence of NH chemical shifts, establishes a 4 - 1 hydrogen bond stabilized type I1 @-turn in the Gly, D-Ala, and Aib peptides, in CDC13 and (CD3)2S0. A positive n-r* CD band at -225-230 nm appears to be characteristic of this structure. For the acyclic Pro-Leu peptide the observation of NOE's for both Pro and Leu C"H resonances on saturation of Leu NH is compatible with a type V bend or consecutive y-turn conformation. In the cyclic disulfide series the Pro-Aib and Pro-D-Ala peptides favor type I1 @-turns, whereas all other peptides adopt type I (111) conformations. All the cyclic disulfides exhibit an intense negative CD band
at -228-230 nm. The results suggest thatgeneralcorrelations between CD spectral type and specific 0-turn conformations may not be obtained. Evidence for solvent-dependent structural changes in the Pro-Aib sequence in both cyclic and acyclic peptides is presented.
194 citations
TL;DR: The optical activity of a number of polypeptides and proteins has been calculated and it is concluded that the 222‐nm band of the α‐helix is a good method for detecting helices in proteins but that the 207‐and 191‐nm bands of the helix will not fit a linear superposition model.
Abstract: Using methods described in a previous publication the optical activity of a number of polypeptides and proteins has been calculated. The systems included the α-helix, the two β-structures, polyproline I, polyproline II, collagen and collagen models, and poly-N-methylalanine. In addition to these orderded structures, calculations were also performed on the α, β and nonperiodic regions of myoglobin, lysozyme, ribonuclease-S and β-chymotrypsin. The α and β structures in prteins differ from the polypeptide models by being very short and partially disordered. It is concluded that the 222-nm band of the α-helix is a good method for detecting helices in proteins but that the 207-and 191-nm bands of the helix will not fit a linear superposition model. The circular dichroism of the so-called β regions of proteins differs markedly from that for ideal β structure because of breakdownin symmetry. As a result estimates of β-structure in proteins based on polypeptide models are not likely to be quantitative.
The theoretical methods give an adequate account of the optical activity of all the ordered polypeptides except polyproline II and collagen and (by inference) the nonperiodic chains in the various proteins. This difficulty is the remaining barrier to a complete theory of the optical activity of the polypeptide backbone in globular proteins.
174 citations
TL;DR: A salt-induced cooperative conformational transition of a synthetic DNA, poly(dG-dC), is reversed by addition of ethidium bromide, and circular dichroism spectra and kinetic data support a model for this cooperative binding that is formally equivalent to the "allosteric" one proposed for oligomeric proteins.
Abstract: A salt-induced cooperative conformational transition of a synthetic DNA, poly(dG-dC), is reversed by addition of ethidium bromide. Binding of the dye at high salt concentrations is highly cooperative. Circular dichroism spectra of the complex and the kinetic data support a model for this cooperative binding that is formally equivalent to the “allosteric” one proposed for oligomeric proteins by Monod et al. Thus, double-helical DNA of at least one defined sequence can undergo a cooperative conformational change in solution, with simple salts and drug molecules as antagonistic effectors. Such transitions may be involved in regulatory phenomena operating directly at the level of nucleic acid structure.
166 citations
TL;DR: These studies indicate that about 20 to 30% of the amino acid residues in the two major HDL apoproteins are involved in a helix-disordered transition on lipid removal or restoration, and the near-ultraviolet CD spectrum is especially sensitive to these lipid-induced structural changes.
158 citations
147 citations
TL;DR: DNA driven into a compact state by excluded volume interactions undergoes a spontaneous rearrangement to an ordered tertiary structure characterized by a circular dichroism spectrum greatly differing from that of DNA in solution.
Abstract: DNA driven into a compact state by excluded volume interactions undergoes a spontaneous rearrangement to an ordered tertiary structure characterized by a circular dichroism spectrum greatly differing from that of DNA in solution.
TL;DR: The data suggest a model that views chromatin condensation as a close packing of superhelical nucleohistone threads but still permits condensed chromatin to respond rapidly to alterations in solvent environment.
Abstract: The degree of chromatin condensation in isolated rat liver nuclei and chicken erythrocyte nuclei was studied by phase-contrast microscopy as a function of solvent pH, K+ and Mg++ concentrations Data were represented as "phase" maps, and standard solvent conditions selected that reproducibly yield granular, slightly granular, and homogeneous nuclei Nuclei in these various states were examined by ultraviolet absorption and circular dichroism (CD) spectroscopy, low-angle X-ray diffraction, electron microscopy, and binding capacity for ethidium bromide Homogeneous nuclei exhibited absorption and CD spectra resembling those of isolated nucleohistone. Suspensions of granular nuclei showed marked turbidity and absorption flattening, and a characteristic blue-shift of a crossover wavelength in the CD spectra. In all solvent conditions studied, except pH < 2 3, low-angle X-ray reflections characteristic of the native, presumably superhelical, nucleohistone were observed from pellets of intact nuclei. Threads (100–200 A diameter) were present in the condensed and dispersed phases of nuclei fixed under the standard solvent conditions, and examined in the electron microscope after thin sectioning and staining Nuclei at neutral pH, with different degrees of chromatin condensation, exhibited similar binding capacities for ethidium bromide. These data suggest a model that views chromatin condensation as a close packing of superhelical nucleohistone threads but still permits condensed chromatin to respond rapidly to alterations in solvent environment.
TL;DR: This protein appears to contain the sites involved in the low affinity binding of Ca2+ to the sarcoplasmic reticulum membrane, and can be produced without a major change in the conformation of the peptide backbone.
TL;DR: The circular dichroism of double-stranded DNA is temperature dependent prior to its melting, and it has been suggested previously that this pre-melt behavior represents a transition from B-DNA to A-DNA, but the data tend specifically to rule out this possibility.
TL;DR: The circular dichroism spectra of many natural DNAs and double‐stranded synthetic polynucleotides were obtained and the eight first‐neighbor contributions to the CD specta of a DNA have been extracted and the CD spectrum may be easily calculated.
Abstract: The circular dichroism spectra of many natural DNAs and double-stranded synthetic polynucleotides were obtained. The eight first-neighbor contributions to the CD spectra of a DNA have been extracted from these data. Therefore, the CD spectrum for any DNA with known first-neighbor frequencies may be easily calculated. For a natural DNA the CD spectrum may be approximated by assuming the first-neighbor frequencies have the most probable values consistent with the base composition. Under favorable conditions, the measured CD spectrum can be used to determine thirteen of the sixteen first-neighbor frequencies of a DNA to ± 0.02 mole percent. The TG, CA, and TA first-neighbor cannot be unambiguously resolved by our method. The accuracy of the first-neighbor frequency analysis depends on the number of different first-neighbors present in the DNA and the extent to which they differ from the most probable value.
The extinction coefficient at 260 nm and the base composition can also be calculated from the CD spectrum.
TL;DR: The substrate-induced conformational change does not result in a change of the molecular weight of the protein as measured by high speed equilibrium centrifugation and sieve chromatography through Bio-Gel P-150.
TL;DR: Equilibrium and kinetic aspects of the interactions of the lac repressor with a series of inducers have been examined and circular dichroism measurements in the peptide region show that the conformational changes do not represent a major rearrangement of repressor secondary structure.
TL;DR: The similarity between the circular dichroism spectra of the polytripeptides and collagen suggests that the observed optical properties arise from the collagen-like triple-helical structure found for both polymers in the solid state.
TL;DR: There is a correlation of the heat of hydration of the cation and the magnitude of theTemperature dependence of the circular dichroism and ultraviolet absorbance of calf thymus DNA and poly dAT were measured in aqueous solutions of various 1–1 electrolytes.
Abstract: The temperature dependence of the circular dichroism and ultraviolet absorbance of calf thymus DNA and poly dAT were measured in aqueous solutions of various 1–1 electrolytes. Although there was very little change in absorbance, the circular dichroism changed dramatically as a function of both temperature and solvent. There is a correlation of the heat of hydration of the cation and the magnitude of the temperature dependence of the circular dichroism. Our results are interpreted in terms of a large number (possibly a continuum) of intermediate secondary structures.
TL;DR: It is suggested that in dimers, though not in higher oligomers or polymers, the stacking equilibrium can be operationally regarded as a two‐state system, and that the meaningful thermodynamic parameters can be extracted by analytical treatment of the melting profiles.
Abstract: Temperature melting profiles of adenylyladenosine and cytidylylcytidine were examined by ultraviolet absorption, circular dichroism, and optical rotatory dispersion. They showed the following characteristics: profiles for different absorption wavelengths are identical as defined by least-squares computed optical and thermodynamic parameters; melting curves obtained by the three spectroscopic methods are likewise in all cases identical by a series of criteria; in terms of the operational equilibrium constant for base-stacking all van't Hoff plots are linear; absorption spectra and circular dichroism curves at a series of temperatures for both dinucleoside phosphates give excellent isosbestic points; a matrix-rank analysis of the family of complete spectra at different temperatures gives a value of two for the numbers of components in both cases. Four criteria are thus fulfilled of a two-state system for the stacking equilibrium. The results are not compatible with a multi-state scheme in which the substates are optically distinguishable. There is no measurable effect of ionic strength up to 1.0. In a presence of high concentrations of lithium chloride the criteria for two-state behavior are no longer fulfilled, and examination of infrared spectra gives evidence of complex formation by this salt, though not by sodium chloride. A destacking profile, similar to that observed on heating, is obtained by progressive addition of ethylene glycol to the solution. It is suggested that in dimers, though not in higher oligomers or polymers, the stacking equilibrium can be operationally regarded as a two-state system, and that the meaningful thermodynamic parameters can be extracted by analytical treatment, of the type here developed, of the melting profiles.
TL;DR: The main Cotton effects observed in the visible region are interpreted as coupling between electric transition dipole moments of bound bilirubin leading to exciton splitting and this explanation is substantiated by computer analysis into Gaussian curves of observed light-absorption and CD spectra.
TL;DR: Sedimentation-velocity and equilibrium ultracentrifugation in 5-8m solutions of urea and guanidinium chloride, and also electrophoresis in sodium dodecyl sulphate-polyacrylamide gel, reveal a dissociation of the native protein molecule into four subunits of similar molecular weight in the range 32500-38000.
Abstract: 1. l-Asparaginases from Erwinia carotovora and Escherichia coli (EC2 enzyme) are both capable of inhibiting and eliminating certain types of tumour cells. The Er. carotovora enzyme is a more basic protein, however, and in contrast with the EC2 enzyme it contains neither tryptophan nor cystine, and disulphide bonds are therefore absent. The molecule is very stable in solution from pH3.0 to about pH12.0, and is somewhat more stable at alkaline pH than is the Esch. coli enzyme. Calculations based on a s(0) (20,w) 7.43S and a sedimentation-equilibrium molecular weight of 135000+/-10000 give a frictional ratio (f/f(0)) of 1.08. The molecular conformation is therefore very compact in solution, and the electron microscope shows the negatively stained molecules as almost spherical particles with a diameter of 7.2+/-0.7nm. 2. Sedimentation-velocity and equilibrium ultracentrifugation, in 5-8m solutions of urea and guanidinium chloride, and also electrophoresis in sodium dodecyl sulphate-polyacrylamide gel, reveal a dissociation of the native protein molecule into four subunits of similar molecular weight in the range 32500-38000. The enzymically inactive subunits can be physically reassembled into an active tetramer when urea is removed by dialysis. Although the subunit structures of the Er. carotovora enzyme and the Esch. coli enzyme molecules are similar, the secondary bonding forces holding the subunits together in the tetramer are somewhat stronger in the Er. carotovora enzyme. 3. The optical-rotatory-dispersion (o.r.d.) parameters that characterize the Cotton effects arising from ordered structure in the molecule are [m'](233)=-3522+/-74 degrees and [m'](200)=9096+/-1700 degrees . These show very marked changes as the secondary structure is disrupted and the molecule dissociates into subunits. A correlation pathway was traced on the basis of o.r.d. parameters and enzyme activity as the polypeptide chains were denatured and renatured (and reconstituted) into active molecules after the dilution of solutions in urea. Subunits resulting from treatment with sodium dodecyl sulphate do not show the typically disordered o.r.d. profile, but nevertheless they are inactive.
TL;DR: In this paper, the helical arrangement of dye molecules dissolved in cholesteric phases leads to a strong circular dichroism in the wavelength range of the solute absorption bands, which yields a simple method to determine relative polarization directions of optical transitions.
TL;DR: The results show that manganese(II) is preferably bound to G · C pairs besides the phosphate groups, and the possible functional role of the differences observed in the complexing of DNA by Mn2+ and Mg2+ are discussed.
Abstract: The complex formation of manganese(II) and magnesium(II) with DNA has been investigated by ultraviolet absorption and circular dichroism (CD) measurements.
G · C-rich DNA shows a difference spectrum in the presence of manganese(II) but not with magnesium(II). The lowering of the melting temperature observed at Mn2+/DNA-phosphorus ratios > 1 increases with increasing G · C content but is diminished in the presence of higher ionic strength.
The circular dichroism spectra of native DNA are greatly affected by manganese(II). Increasing Mn2+ concentration decrease the CD maximum of G · C-rich DNA at 270 nm while Mg2+ does not change the CD curve. Contrary to the ordered double helical form the CD spectra of denatured DNA are unaltered. The manganese(II)-induced perturbation of the circular dichroism of native DNA becomes increased with increasing G · C content and reaches a saturation level around 50 mol % guanine-plus-cytosine.
The results show that manganese(II) is preferably bound to G · C pairs besides the phosphate groups. The CD spectrum of protonated G · C-rich DNA is strongly changed by manganese(II) which indicates competition between the divalent metal ion and the proton at the binding site. In agreement with the behavior of methylated DNA the proton displacement by Mn2+ from G · C pairs suggests that Mn2+ coordinates with the N-7 position of guanine. The spectral changes of the circular dichroism depend also on the shielding of phosphate groups by sodium ions. The results of the circular dichroism which indicate G · C selective conformational changes of the DNA are interpreted by tilting of the bases of locally Mn2+ chelated regions. The possible functional role of the differences observed in the complexing of DNA by Mn2+ and Mg2+ are discussed.