Showing papers on "Circular dichroism published in 1971"
TL;DR: It appears that ω is capable of introducing a “swivel” reversibly into a DNA, and a plausible mechanism is postulated.
696 citations
316 citations
TL;DR: The rotatory contributions can be written as X = ΣfiXi, where the subscripts i = H, β and R represent the fractions of the helix, β-form and unordered form.
315 citations
TL;DR: The circular dichroic spectra of molluscan and arthropod oxyhemocyanins are qualitatively and quantitatively different and indicate fundamental differences in the oxygen binding sites of these related proteins.
Abstract: 1. 1. The circular dichroic (CD) spectra of molluscan and arthropod oxyhemocyanins are qualitatively and quantitatively different. 2. 2. Molluscan oxyhemocyanins have three CD bands in the visible, a positive band near 450 nm, a negative band near 570 nm and a positive band near 710 nm. 3. 3. Arthropod oxyhemocyanins have only two visible CD bands, both positive, near 490 and 610 nm. 4. 4. Both types have a negative CD band near 340 nm. 5. 5. In the region between 260–300 nm, the CD of molluscan hemocyanins is positive, that of arthropods negative. 6. 6. These data indicate fundamental differences in the oxygen binding sites of these related proteins.
229 citations
TL;DR: H+ ion titration studies confirm previous conclusions from optical activity studies that high concentrations of calcium ion do not significantly diminish the interaction of the hormones with bovine neurophysin.
129 citations
128 citations
128 citations
115 citations
TL;DR: The absorption and circular dichroism spectra of (+) 3‐methylcyclopentanone to 1350 A are presented.
Abstract: We have developed a circular dichroism spectrometer which will make measurements in the ultraviolet to 1350 A. It is built primarily from commercially available components and is particularly simple in design. The instrument is linear and has a noise level over most of its range of less than 1×10−5 OD units for a 16 A spectral slitwidth and 10 sec time constant. The absorption and circular dichroism spectra of (+) 3‐methylcyclopentanone to 1350 A are presented.
108 citations
TL;DR: Spectrophotometric, sedimentation, infrared, optical rotatory dispersion, and circular dichroism methods have been used to demonstrate the structural changes in DNA induced by the interaction of copper(II) with bases and to elucidate the complex binding sites.
Abstract: Spectrophotometric, sedimentation, infrared, optical rotatory dispersion (ORD), and circular dichroism (CD) methods have been used to demonstrate the structural changes in DNA induced by the interaction of copper(II) with bases and to elucidate the complex binding sites. As shown by the electrolyte-induced reversion (addition of salts) of temperature-denatured copper DNA the effectiveness of re-formation of the double-stranded structure depends on the temperature, copper(II) ion concentration, and on the base composition of the DNA. Exposure of heat-denatured copper DNA to higher temperatures decreases the reversion effect on addition of electrolyte. The results indicate that a greater fraction with a cooperative transition appears on heating DNA to 80 or 100°C at a Cu2+/DNA-P ratio of 2 : 1 than at a Cu2+/DNA-P ratio of 1 : 1. With AT-rich copper DNA, reversion to the native DNA structure was not observed. Selective methylation of guanine residues in DNA also affects the electrolyte-induced reversion, indicating the importance of GC pairs for copper(II) binding and the reversion to the native structure. Temperature-denatured copper DNA shows an increased sedimentation coefficient Which decreases again after electrolyte-induced reversion. This change in s is reduced by selective methylation of DNA. Complex formation between copper(II) and the bases is accompanied by a conformational change of the DNA double-helical structure as demonstrated by ORD and CD experiments. The ORD profile of GC-rich DNA is much more affected by copper(II) than that of AT-rich ones. Even at very low copper(II) concentrations, e.g., at 0.02 and 0.2 Cu2+/DNA-P, the ORD and CD measurements exhibit conformational changes of the DNA secondary structure at room temperature. By comparing the infrared spectra of deoxynucleosides with that of DNA of different GC content it has been shown that both guanine and cytosine are involved in the formation of the complex of copper(II) with DNA. N-7 and O at C-6 in guanine and N-3 as well as O of C-2 in cytosine are discussed as the most probable binding sites in DNA. A binding model for the coordination of the copper(II) ion between guanine and cytosine of the opposite strands is suggested. The results are in good agreement with the assumptions and predictions made by Eichhorn and Clark about the complexing of copper(II) with DNA. The recent proposal made by Schreiber and Daune about an interaction of the type guanine–Cu2+–guanine cannot be excluded as an additional kind of coordination of copper(II) in DNA.
102 citations
TL;DR: A conformational analysis was carried out on a series of L‐isoleucine oligomers having the general formula BOC‐(Ileu)n‐OMe, indicating that these oligomers form β‐conformations beginning at the heptamer.
Abstract: A conformational analysis was carried out on a series of L-isoleucine oligomers having the general formula BOC-(Ileu)n-OMe (n = 2–8). These oligopeptides were examined in trifluoroethanol, trifluoroethanol-acid and mixed organic-water media. The results indicate that these oligomers form β-conformations beginning at the heptamer. The stability of the β-conformations was found to be greater than those formed by oligopeptides derived from L-alanine.
TL;DR: The variation of the magnitude of the visible and near—ultraviolet CD spectra of ethidium bromide—DNA complexes with the amount of ligand bound (r) suggests a common binding position with profiavine, while 4‐ethyl‐9‐aminoacndine complexed to DNA showsCD spectra not distinguishable from those of 9‐aminnoacnidmc in both thevisible and ultraviolet.
Abstract: The circular dicrosim (CD) spectra of complexes of DNA with ethidiun bromnide, profiavine, 9-aminoacridine and 4-etliyl-9-amino-acridine have been determined between 220 and 450 nm, the range lieing extended to 600 nm for ethidiufm bromide. The variation of the magnitude of the visible and near—ultraviolet CD spectra of ethidium bromide—DNA complexes with the amount of ligand bound (r) suggests a common binding position with profiavine. On the other hand, 4-ethyl-9-aminoacndine complexed to DNA shows CD spectra not distinguishable from those of 9-aminnoacnidmc in both the visible and ultraviolet. The interpretation of these results with respect to the stereochemistry of the DNA-ligand complexes is discussed.
TL;DR: The prominent positive ellipticity of deoxygenated human hemoglobin at 430 nm was decreased by either carboxypeptidase digestion or dialysis against deionized water, which led to a loss of heme-heme interaction and to an increase in the oxygen affinity, without changing the gross structure of the molecule.
TL;DR: The high ammonia level of the acid hydrolyzate and the high amide level seen in Pronase digests suggest that a very large percentage of the dicarboxylic acids may be present in the protein as the corresponding amides.
Abstract: Publisher Summary This chapter discusses the physical, chemical, and catalytic properties of spleen acid deoxyribonuclease (DNase). The high ammonia level of the acid hydrolyzate and the high amide level seen in Pronase digests suggest that a very large percentage of the dicarboxylic acids may be present in the protein as the corresponding amides. Glucosamine and mannose are present in the protein; in the tryptic digests, the glucosamine and neutral sugar residues are found on a single peptide spot. No free sulfhydryl groups can be detected in acid DNase, both native and denatured; therefore, the eight half-cystine residues must form four disulfide bridges. Optical rotatory dispersion, circular dichroism, and infrared spectra of acid DNase have shown that the enzyme contains little α-helix; antiparallel pleated sheet β-structure is probably present in the molecule. Some chemical and physical results seem to suggest that acid DNase may have a dimeric structure. When the enzyme is reduced, carboxymethylated, digested with crystalline trypsin and mapped, 17-19 peptides are found as opposed to 32-34 arginine + lysine residues present in each enzyme molecule of MW = 38,000. Arginine, tryptophan, and histidine peptides are found in half, or less than half, the number of the respective amino acids in the supposedly dimeric protein. Other results also suggesting a dimeric Structure come from sedimentation studies.
TL;DR: Improved circular dichroism curves are reported for mitochondria and red blood cell ghosts and previously proposed details of membrane structure based on the “red shift” are not supported by the corrected spectra.
TL;DR: The circular dichroism of glycosaminoglycans and ganglioside in distilled water are described, showing two bands in the region of amide and carboxyl transitions, common to all polymers and the amino sugar derivatives.
Abstract: The circular dichroism of glycosaminoglycans and ganglioside in distilled water are described, showing two bands in the region of amide and carboxyl transitions. The first, negative hand is common to all polymers and the amino sugar derivatives. The characteristics of the second band depend upon polymer structure. Those containing 4–1-linked amino sugars show a second, positive, resolved band about 190 mμ, while those with 3–1-linked amino sugars show a second, negative band less resolved from the first usually ≤185mμ, but clearly centered at 188mμ for dermatan sulfate. Ultraviolet optical absorption from 300 to ∼183 mμ showed inflection regions around 190 mμ for most compounds.
TL;DR: It is demonstrated that magnetic circular dichroism is a tool for resolving overlapping CD and absorption bands in the region of the copper d → d transition in erythrocuprein.
TL;DR: Urea inhibited binding of vitamin D-induced calcium-binding protein and divalent cations shown to compete with 45Ca for the binding site or depress binding by another mechanism were Zn++, Cd++, Mn++, and Fe++; under the conditions used, Co++ and Ni++ were ineffective.
TL;DR: These results, together with substantial supporting evidence, show that the covalent binding of N-2-acetylaminofluorene causes important changes in the conformational properties of oligonucleotides in aqueous solution.
TL;DR: The results indicate that at low temperature, polyuridylic acid adopts a double-helical structure resulting from the folding of the molecule on itself (a single hairpin), and upon heating, branching takes place leading to the formation of multi-hairpins.
TL;DR: The thermal denaturation of the A and B variants of bovine β-lactoglobulin has been examined using optical rotatory dispersion and sedimentation velocity techniques and an equation is derived which describes the time dependence of optical rotation in terms of parameters relevant to a system involving two consecutive first order reactions.
TL;DR: The results demonstrate that complex formation in aqueous solutions involves a stacking of the aromatic rings of both molecules, and the role that could be played by tyrosine residues in enzymes or proteins in their interaction with nucleic acids is discussed.
TL;DR: The results indicate that the double helix in a superhelical DNA is perturbed somewhat due to the bending and torsional forces in such a molecule.
Abstract: The circular dichroism (CD) spectra of a number of superhelical DNA's have been measured The introduction of negative superhelical turns causes an increase in magnitude of the positive band around 280 mμ, while the trough around 250mμ is little affected For two samples of λb2b5c DNA (20 Mdalton) containing different number of negative superhelical turns, the magnitude of the positive band relative to that of the nicked control increases with increasing number of superhelical turns In 2M NaCl, the small (145 Mdalton) superhelical DNA from E coli 15 shows an unusually large difference in CD compared with that of the same DNA with a few single-chain scissions per molecule This large difference is not observed in a medium containing p 011M NaCl These results indicate that the double helix in a superhelical DNA is perturbed somewhat due to the bending and torsional forces in such a molecule The magnitude of such structural alteration seems to depend on the number of superhelical turns per unit length, the size of the DNA molecule, as well as the ionic medium
TL;DR: No significant variations occur in the secondary structure of the protein as reflected by the constancy of the far ultraviolet CD spectrum with ligand complexation, and exploration of the CD aromatic fine structure as a function of pH indicates that both tyrosine and tryptophan chromophores are involved.
TL;DR: Inspection of a recently proposed model for bovine α-lactalbumin indicates the proximity of a number of lysyl, glutamyl, and aspartyl side chains, in accord with the hypothesis that breaking of charge pairs (amino and carboxylic acid groups) may initiate the structural change.