Showing papers on "Circular dichroism published in 1969"
TL;DR: Optical rotatory dispersion and circular dichroism measurements on the highly purified rhodopsin preparation indicate that native rhodopin possesses approximately 60% helical structure and one-fifth of the helical content is lost on irreversible bleaching.
265 citations
TL;DR: The circular dichroism (CD) spectrum of an unordered polypeptide chain does not correspond, as has been assumed heretofore, to that of a charged chain such as poly‐L‐glutamic acid or poly‐ L‐lysine, as well as two fibrous proteins and a globular protein.
Abstract: The circular dichroism (CD) spectrum of an unordered polypeptide chain does not correspond, as has been assumed heretofore, to that of a charged chain such as poly-L-glutamic acid or poly-L-lysine. The latter have been shown to have locally ordered structures with characteristic CD spectra. We have now obtained CD spectra of the unordered forms of the above synthetic, polypeptides, as well as of two fibrous proteins (collagen and feather keratin) and a globular protein (myoglobin). These spectra are all similar to that of unordered polyproline, having a negative band in the vicinity of 2000 mμ and no additional bands at longer wavelengths. The lack of structural uniqueness of the unordered polypeptide chain is emphasized by these studies.
258 citations
209 citations
TL;DR: A particularly simple theory of circular dichroism is described and applied to the polynucleotides as mentioned in this paper, which works surprisingly well and predicts the conservative spectrum of DNA and the more intense non-conservative spectrum of RNA.
Abstract: A particularly simple theory of circular dichroism is described and applied to the polynucleotides. It works surprisingly well and predicts the conservative spectrum of DNA and the more intense nonconservative spectrum of RNA. The anomalously low intensity of the CD of the nucleic acids is shown to be a natural consequence of the cancellation of the rotational strengths of the many CD bands. The theory's many successes and predictions as well as its weaknesses are discussed.
188 citations
163 citations
TL;DR: The phases present in a variety of protein–lipid–water systems have been identified and their structure established by X-ray diffraction, and correlations between optical properties and structure are discussed.
Abstract: The phases present in a variety of protein–lipid–water systems have been identified, and their structure established by X-ray diffraction. A spectrophotometric and circular dichroism analysis has been carried out on phases of known structure, and correlations between optical properties and structure are discussed.
163 citations
157 citations
TL;DR: It is concluded that almost the entire amino acid sequence of nuclease is essential to determine unique folding and that the native conformation of nUClease cannot be formed during synthesis until the polypeptide chain has been extended beyond Residue 126.
153 citations
TL;DR: Evidence is provided for the mutual role of the protein and lipids in determining the structure, and perhaps the immunological specificity, of serum lipoproteins in Sprague-Dawley rats.
152 citations
TL;DR: A major hysteresis effect occurs in the pH dependence of Mw and s20,w corresponding to the hysteResis previously observed for the hydrogen ion titration of the protein.
137 citations
TL;DR: Study of a series of gamma-ethyl-L-glutamate oligopeptides by circular dichroism and 220 MHz nuclear magnetic resonance spectroscopy found changes in chemical shifts for the amide protons consistent with the onset of helicity at the heptamer in the solvents noted above.
Abstract: We studied the conformation of a series of γ-ethyl-L-glutamate oligopeptides by circular dichroism and 220 MHz nuclear magnetic resonance spectroscopy. By use of the first technique we noted enhancement of the n → π* and splitting of the π → π* transitions commencing with the heptamer in trimethylphosphate and trifluoroethanol. With the second method we found changes in chemical shifts for the amide protons consistent with the onset of helicity at the heptamer in the solvents noted above. When DMSO-d6 is used as a solvent, no such chemical shift changes occur because the oligopeptides do not assume helical conformations.
TL;DR: It is reported that the circular dichroism pattern of soluble elastin most nearly resembles that of disordered proteins and polypeptides whereas the circular adjacency pattern of the coacervate (a mucilaginous precipitate) is characteristic of those obtained for the highly helical proteins andpolypeptide.
Abstract: WHEN fibrous elastin is rendered water soluble by partial hydrolysis the product, α-elastin, undergoes a temperature elicited coacervation which is readily reversible1,2. Below room temperature α-elastin is soluble in dilute aqueous buffers in the region of its isoelectric point. On raising the temperature to 37° C a phase separation or coacervation occurs. In this communication we wish briefly to report that the circular dichroism pattern of soluble elastin most nearly resembles that of disordered proteins and polypeptides whereas the circular dichroism pattern of the coacervate (a mucilaginous precipitate) is characteristic of those obtained for the highly helical proteins and polypeptides. A calculation based on model polypeptides and myoglobin and on corrections for dampening of CD patterns due to absorption flattening and dispersion distortions3 implies an approximate 50 per cent α-helical content for the protein in the coacervate.
TL;DR: The ORD and CD of din nucleoside phosphates and trinucleoside diphosphates are sequence-dependent; the positions of the extremes and their magnitudes vary among the isomers, even though the general spectra are very similar.
Abstract: Publisher Summary Optical Rotatory Dispersion and Circular Dichroism of Nucleic Acids11This work was supported by grunts from the United States Public Health Service (GM-K3-3441, GM-10880, and HE-06285) This chapter discusses the optical rotatory dispersion (ORD) and circular dichroism (CD) of nucleic acids. It discusses the principles of ORD and CD. It presents the optical activity of mononucleosides and mononucleotides, which are in a class by themselves, and discusses the similarities between ORD and CD between oligonucleotides and polynucleotides and the differences between DNA and RNA. The ORD and CD of dinucleoside phosphates and trinucleoside diphosphates are sequence-dependent; the positions of the extremes and their magnitudes vary among the isomers, even though the general spectra are very similar. Thus, optical activity can become a new means for determining the base sequence in oligonucleotides.
TL;DR: In this article, the CD spectra of a number of rigid aromatic compounds containing an asymmetric center adjacent to the aromatic ring are reported, and a quadrant rule is proposed to predict the absolute configuration of molecules possessing an asymptotic center.
TL;DR: Circular dichroic spectra of glucagon confirm that in dilute aqueous solutions about 10–15% α-helix is present which increases to about 35% α -helix at concentrations greater than 10 mg/ml.
TL;DR: Theoretical and experimental advances have led to a reassessment of the interpretation of optical rotatory dispersion and circular dichroism of nucleic acids, proteins and related compounds.
Abstract: Theoretical and experimental advances have led to a reassessment of the interpretation of optical rotatory dispersion and circular dichroism of nucleic acids, proteins and related compounds. The present state of the field is reviewed in this article.
TL;DR: It is shown that the portion of the RNase A spectrum in the peptide-absorbing region may be fitted by assuming that 11.5% of the residues are in an α-helical conformation and 33% in a β-conformation, and a larger, negative, band at 275 mµ is shown, in agreement with others, to arise predominantly from tyrosine residues.
TL;DR: It is concluded that the presence of an unsubstituted 2′-hydroxyl group in poly A is not essential for the stabilization of the double-stranded conformations of poly A in acidic solutions, for the partially-ordered single-Stranded conformation of poly B at neutrality or for the double -stranded complex ofpoly A with poly U.
TL;DR: From theoretical considerations, it is shown that the 280 mμ band is not an exciton component of the strong π–π* transition at 260 mμ in adenine, and must be assigned to a distinct absorption, not previously reported, which it is suggested arises from an n– π* transition.
Abstract: Circular dichroism (CD) curves are reported for poly dA, (pdA)6, (pdA)2, poly A, ApAp, ApA, AMP, dApA, pdApA, A-2′-O-methyl pA, and A-2′-O-methyl pAp. Analysis of these curves indicated the presence of single CD bands at 228–230 mμ and at 278–280 mμ in oligomers longer than dinucleotides. In the case of dinucleotides and mononucleotides (from the literature, in addition to those studied here), the 230 mμ CD of band appears but the 280 mμ CD band does not. We assign the 230 mμ band to a very weak π–π* transition at this wavelength. From theoretical considerations, we show that the 280 mμ band is not an exciton component of the strong π–π* transition at 260 mμ in adenine. We conclude that the 280 mμ CD band must be assigned to a distinct absorption, not previously reported, which we suggest arises from an n–π* transition. The fact that the n–π* CD band at 280 mμ is not seen in mononucleotides or dinucleotides is ascribed to solvation of the adenine ring by water, which shifts the band to shorter wavelengths. Therefore, only interior residues of oligomers have the 280 mμ band, and the optical activity of a polymer cannot be computed from that of a dinucleotide, by using a nearest-neighbor approximation. The existence of this end effect hag been tested, by taking it into account in computing the rotational strengths of the 278 mμ n–π* transition for several oligomers; it is pointed out that a more sensitive test of this end effect would require CD data for the oligo dA series of 3 to 5 residues. We speculate about the structural and optical differences between poly dA and poly A, and point out the need for a theoretical treatment of n–π* Cotton effects in polynucleotides.
TL;DR: In the past few years, applications of physical techniques to studies of membrane structure have increased greatly and they have begun to provide more precise structural parameters for membranes and also some indication of the physical states of the molecular constituents in the membranes.
Abstract: Applications of physical techniques to studies of membrane structure have increased greatly in the past few years and they have begun to provide more precise structural parameters for membranes and also some indication of the physical states of the molecular constituents in the membranes. Direct measurements of membrane features have been made by electron microscopy and by X-ray diffraction methods. Spectroscopic techniques especially infrared absorption, nuclear magnetic resonance absorption and optical rotatory dispersion and circular dichroism measurements have provided additional data relating to the physical states of the molecular components in the membranes.
TL;DR: In this article, the exciton model for optical activity and the perturbing effects of π-electron exchange between the ligands and the metal ion were analyzed in terms of exciton spectra for tris-bipyridyl and phenanthroline complexes.
Abstract: Absorption and circular dichroism spectra are reported for the tris-bipyridyl and the -phenanthroline (phen) complexes of iron(II), ruthenium-(II) and -(III), and osmium-(II) and -(III). The results are analysed in terms of the exciton model for optical activity and the perturbing effects of π-electron exchange between the ligands and between the ligands and the metal ion. It is found that the principal spectroscopic and stereochemical conclusions of the exciton theory are qualitatively unaffected by the perturbations, provided that the complete monopole exciton energy is considered rather than that evaluated in the point-dipole approximation. Metal–ligand π-bonding is shown to be more important in the di- than the tri-valent complexes, the apparent exciton-splitting being diminshed in both cases. Ligand–ligand bonding may enhance or decrease the exciton splitting, depending upon the symmetry of the ligand π-orbitals with respect to rotation about the two-fold (short) ligand axis. The p-band in the spectra of bipyridyl and phenanthroline is found to be predominantly long-axis polarised, although there is a short-axis component in the latter case due to the overlapping α-band. The higher energy β-band is shown to be short-axis polarised in both cases. The main circular dichroism of the complexes in the visible region is found to reflect the exciton dichroism of the u.v. region, owing to the combination of long-axis polarised charge-transfer transitions with ligand excitations of the same polarisation. The optical isomers studied are assigned the M(C3) stereochemical configuration established for (–)-[Fe phen3]2+ by X-ray analysis.
TL;DR: It is shown that the red shift and decrease in amplitude of the CD extrema of particulate systems correlate with changes in the intensity of scattered light and with the extent of absorption flattening as measured, respectively, at wavelengths where significant absorption does not occur and at wavelengths corresponding to major absorption bands.
TL;DR: The data suggest that the architecture of membrane proteins is strongly dependent upon apolar lipid-protein and/or lipid-sensitive protein-protein interactions.
Abstract: The general relations between protein conformation and the optical activity of peptide chromophores are outlined and applied to the analysis of the optical rotatory dispersion and circular dichroism of the plasma membranes of human erythrocytes and Ehrlich ascites carcinoma cells It is concluded that the proteins of these membranes are "globular" and that they have considerable helical content The spectroscopic consequences of perturbing the membranes with phospholipase C, phospholipase A, lysolecithin, and sodium dodecyl sulfate are examined in the light of the effects of these agents upon certain enzymatic and physical properties of the membranes and upon their proton magnetic resonance spectra The data suggest that the architecture of membrane proteins is strongly dependent upon apolar lipid-protein and/or lipid-sensitive protein-protein interactions
TL;DR: The far ultraviolet circular dichroism is consistent with the structure being a triple helix of the type present in collagen and suggested for (Gly-Pro-Ala)n in the solid state.
TL;DR: From comparison of the absorption spectra of proflavine complexed with calf thymus and T2 DNA, it is concluded that stacking of the dyes external to the double helix is comparatively much weaker with T2 DXA, probably because of its glucosylation.
Abstract: We report studies of the optical properties of the proflavine–DNA complex, using absorbance and circular dichroism spectroscopy. From comparison of the absorption spectra of proflavine complexed with calf thymus and T2 DNA, we conclude that stacking of the dyes external to the double helix is comparatively much weaker with T2 DXA, probably because of its glucosylation. Several sources are found for the circular dichroism induced in proflavine when it is complexed with DNA. There is a relatively weak circular dichroism induced when the dye is infinitely dilute on the DNA lattice; this presumably arises from the environmental asymmetry of the binding site. Stronger circular dichroism effects are induced by interaction of intercalated and stacked dyes; studies with T2 DNA, for which stacking seems to be blocked, permit a tentative resolution of effects due to the two modes of binding. One recurring theme of these studies is the observation that the optical properties are quite dependent on environment. The most dramatic example is a strong variation with salt concentration of the amplitude of the circular dichroism induced in the isolated (intercalated) monomer by the surrounding DNA. This suggests that the structure of the intercalated complex is quite sensitive to external conditions.
TL;DR: A kinetic study of the reaction of xanthine oxidase in solution with the reducing substrate o-phenanthroline reveals that the initial increase in flavin radical parallels the increase in absorbance at 620 mµ, thus supporting the identification of the flavin as the neutral species and similar kinetic data are observed for the Flavin and molybdenum and the iron.