Showing papers on "Circular dichroism published in 1968"
349 citations
TL;DR: The effects of several commonly employed fixatives on the three-dimensional conformations of two soluble proteins and the protein of intact red blood cell membranes have been studied by means of circular dichroism measurements in the spectral region of the peptide absorption bands.
Abstract: The effects of several commonly employed fixatives on the three-dimensional conformations of two soluble proteins and the protein of intact red blood cell membranes have been studied by means of circular dichroism measurements in the spectral region of the peptide absorption bands. The fixatives used produced significant and parallel conformational changes in all of the proteins, in the increasing order: glutaraldehyde; OsO4; glutaraldehyde followed by OsO4; and KMnO4. The last two treatments obliterated most of the helical character of the proteins. The significance of these observations to the preparation of specimens for electron microscopy is discussed.
169 citations
148 citations
TL;DR: Treatment of human red blood cell membranes with phospholipase C releases 68 to 74 percent of the total membrane phosphorus into solution, through hydrolysis of membrane phospholips to diglycerides and water-soluble phosphorylated amines, and the membrane remains intact in phase microscopy.
Abstract: Treatment of human red blood cell membranes with phospholipase C releases 68 to 74 percent of the total membrane phosphorus into solution, through hydrolysis of membrane phospholipids to diglycerides and water-soluble phosphorylated amines. In spite of this drastic change, the membrane remains intact in phase microscopy, and the average protein conformation in the membranes, as determined by circular dichroism measurements in the ultraviolet, is unaffected. These results are readily explained by a model of membrane structure that is stabilized by hydrophobic interactions and in which the polar and ionic heads of lipids are on the outer surfaces of the membrane, in contact with the bulk aqueous phase and accessible to the action of phospholipase C.
135 citations
133 citations
132 citations
TL;DR: The Kronig-Kramers transforms which relate circular dichroism and optical rotatory dispersion are valid and shifts and decreases in magnitude observed with one physical measurement will be reflected in the other.
124 citations
TL;DR: The principles of circular dichroism and of optical rotatory dispersion are described in this article, and examples illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products.
Abstract: The principles of circular dichroism and of optical rotatory dispersion are described. Examples are given to illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products. Some limitations of the octant rule are mentioned.
112 citations
107 citations
TL;DR: The tetrapeptide l-aspartyl- l-threonyl-l-histidyl-l -lysine was shown by titration, absorbance, and circular dichroism measurements to form an equimolar complex with copper(II) that has substantially the properties of the complex of peptide (1–24) containing 1 eq of copper( II) ion.
104 citations
TL;DR: Human serum low density lipoprotein of d 1.019-1.063 (LDL(2) treated with succinic anhydride at pH 7.5-8.0 showed the same chemical composition, hydrodynamic properties (flotation and sedimentation coefficients, intrinsic viscosity) and optical properties (circular dichroism) as untreated LDL(2).
TL;DR: Oxytocin and its analogues exhibit a band which can only be due to disulfide and which, in two other cases, may be contributed to by tyrosine, and interactions among residues within these peptides and of possible conformational differences among the derivatives examined.
TL;DR: The results suggest that the active sites are similar in both isoenzymes, but that small differences do exist, and that the isoenZymes have an appreciable helical content.
TL;DR: Ritonuclease A and ribonuclease S exhibit no positive 240 mµ circular dichroism maximum in solutions below pH 2 and 3.5, respectively; this pH dependence suggests that a side chain carboxylic acid residue interaction occurs.
TL;DR: The circular dichroic absorption spectra of the phenol and indole chromophores have been determined in the near ultraviolet in water, dioxane, and dimethyl sulfoxide with the diketopiperazines of tyrosine and tryptophan.
TL;DR: Attention is largely focused on the optical rotatory dispersion and circular dichroism spectra of these proteins in the near ultraviolet region, where characteristic aromatic side‐chain bands occur.
Abstract: We present here a brief analysis of ultraviolet isotropic absorption and related circular dichroism of the n–π* and π–π* transitions for the peptide (amide) chromophore in the 185–240 mμ region. Investigations by ultraviolet absorption and circular dichroism techniques on natural amino acids with aromatic chromophores in their side chains are also reported. By taking into account both the peptide and aromatic transitions we discuss the conformational studies of proteins with aromatic side-chain effects. Our attention is largely focused on the optical rotatory dispersion and circular dichroism spectra of these proteins in the near ultraviolet region, where characteristic aromatic side-chain bands occur. The 185–240 mμ region is also discussed when evidence exists of overlapping Cotton effects of aromatic and peptide groups.
TL;DR: The circular dichroism spectra of the mammalian-type cytochromes c of horse, beef, chicken, turtle, and Pseudomonas aeruginosa are grossly similar to each other and it is likely that the environment of the heme group in the reduced form of cytochrome c remains invariant.
TL;DR: The magnetic circular dichroism (MCD) of IrCl62−, IrBr62− and RuBr63− have been measured through the visible and near ultraviolet as discussed by the authors.
Abstract: The magnetic circular dichroism (MCD) of IrCl62−, IrBr62−, and RuBr63− have been measured through the visible and near ultraviolet. Analysis leads to new assignments of the ligand‐to‐metal (t2g) charge‐transfer bands. In particular, the conventional order of the first two allowed charge‐transfer states is reversed so that the 2T1u state lies at lower energy than 2T2u.
TL;DR: Water‐soluble block copolymers of L‐valine and D, L‐lysine were prepared and the short valine block was found to be in the right‐handed α‐helical conformation in 98% aqueous methanol, in water, the polymer appears to be a dimer, with thevaline block being involved in the formation of an intermolecular β‐structure.
Abstract: In order to test theoretical predictions that poly-L-valine can exist in an α-helical conformation, water-soluble block copolymers of L-valine and D, L-lysine were prepared. By carrying out the synthesis on a resin support (with the use of N-carboxyanhydrides) contamination of the individual blocks by any unreacted monomer from the previous block was avoided. A single glycine residue was incorporated at the C-terminus of the chain for use in amino acid analyses. Using optical rotatory dispersion and circular dichroism criteria, about 50% of the short valine block of (D, L-lysine HCl)18-(L-valine)15-(D, L-lysine-HCl)16-glycine was found to be in the right-handed α-helical conformation in 98% aqueous methanol, in water, the polymer appears to be a dimer, with the valine block being involved in the formation of an intermolecular β-structure.
TL;DR: For the first time, the circular dichroism spectra in which the n‐π* peptide band of a left‐handed helical conformation is almost completely evident are reported.
Abstract: A series of copolymers of β-p-nitrobenzyl L-aspartate with β-benzyl L-aspartate and with β-mcthyl L-aspartatc in helix-supporting and helix-breaking conditions have been reexamined by using ultraviolet isotropic, absorption, optical rotatory dispersion, and circular dichroism techniques. Many different conformations are apparent, depending on solvent and temperature. Chloroform, trifluoroethanol, and methylene dichloride support the left-handed helical conformation of the copolymers containing less than about 20 mole-% nitroaromatic residues and the right-handed helical conformation of the copolymers containing more than approximately 30 mole-% nitroaromatic residues. In trifluoroacetic acid all the copolymers are in a random-coil conformation. In hexa-fluoroacetone trihydrate and in trimethyl phosphate, the copolypeptides with low nitroaromatic residues content are predominantly in a disordered conformation, while those with high nitroaromatic residues content show a right-handed helical array. Reversible helix-ramlom-coil transitions are observed with increasing temperature in trimethyl phosphate. An example of right-handed-left-handed helix reversible transition with temperature is reported in a chloroform-trimethyl phosphate (2:1) mixture. Nitrobenzyl-nilrobenzyl side-chain interactions in chloroform, but not in trifluoroacetic acid or in trimethyl phosphate, have been confirmed. For the first time we report the circular dichroism spectra in which the n-π* peptide band of a left-handed helical conformation is almost completely evident.
TL;DR: Optical rotatory dispersion and circular dichroism have been used to investigate the protonation of guanosine and some of its analogues and an inversion of the principal Cotton effect and the dichroic band is observed below the acid pK.
TL;DR: The optical rotatory dispersion and circular dichroism of a double-stranded ribonucleic acid from rice dwarf virus have been measured, providing evidence of a doublestranded helical structure.
TL;DR: The ultraviolet circular dichroism in nucleic acid structural analysis is described and investigates whether nucleic acids, due to their conformational dissymmetry, give rise to Cotton effects in the ultraviolet and whether these can be used for structural investigation.
Abstract: Publisher Summary This chapter describes the ultraviolet circular dichroism in nucleic acid structural analysis and investigates whether nucleic acids, due to their conformational dissymmetry, give rise to Cotton effects in the ultraviolet and whether these can be used for structural investigation. Ordinary spectrophotometry is a necessary supplementation of circular dichroism (CD) work for the determination of hypochromicity or other forms of difference spectra as additional criteria of structural features in case of proteins and nucleic acids. The α-helix is considered as an exciton, thought to give rise to a splitting of the major absorption band of the peptide structure (around or below 200 mμ) into two spectral components, which are polarized parallel and perpendicular to the longitudinal axis of the helix. The CD spectrum of peptides known to be helically structured reveals a positive CD band at about 194 mμ and a negative band at 207 mμ, with rotational strengths of about 80×10–40 and –30×10–40, respectively, ascribed to the exciton structure. These features have been found in few proteins that have been investigated such as apomyoglobin, myosin, actin, and rhodopsin. One can anticipate a fruitful further development of this field, which is of interest also to nucleic acid research inasmuch as the structural aspects of protein–polynucleotide interactions will be revealing.
TL;DR: In this article, the same set of bands generated both the absorption and the circular dichroism spectra by the adjustment of the signs and the heights of the bands, while keeping the positions and the band widths constant.
TL;DR: Fractionation of sonic disrupted mitochondria and experiments on acetone-treated mitochondria show that the spectral shift associated with the membrane fraction is not removed by lipid extraction, and the spectral changes that arise from changes in metabolic state and ultrastructure reflect conformational changes of the inner membrane proteins.