NMR Relaxation Rates (nmr + relaxation_rate)

Distribution by Scientific Domains

Selected Abstracts

15N relaxation study of the amyloid ,-peptide: structural propensities and persistence length

Jens Danielsson
Abstract The dynamics of monomeric Alzheimer A,(1,40) in aqueous solution was studied using heteronuclear NMR experiments. 15N NMR relaxation rates of amide groups report on the dynamics in the peptide chain and make it possible to estimate structural propensities from temperature-dependent relaxation data and chemical shifts change analysis. The persistence length of the polypeptide chain was determined using a model in which the influence of neighboring residue relaxation is assumed to decay exponentially as a function of distance. The persistence length of the A,(1,40) monomer was found to decrease from eight to three residues when temperature was increased from 3 to 18 C. At 3 C the peptide shows structural propensities that correlate well with the suggested secondary structure regions of the peptide to be present in the fibrils, and with the ,-helical structure in membrane-mimicking systems. Our data leads to a structural model for the monomeric soluble ,-peptide with six different regions of secondary structure propensities. The peptide has two regions with ,-strand propensity (residues 16,24 and 31,40), two regions with high PII-helix propensity (residues 1,4 and 11,15) and two unstructured regions with higher mobility (residues 5,10 and 25,30) connecting the structural elements. Copyright 2006 John Wiley & Sons, Ltd. [source]

Carbon-13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates,

Jinfa Ying
Abstract Knowledge of 13C chemical shift anisotropy (CSA) in nucleotide bases is important for the interpretation of solution-state NMR relaxation data in terms of local dynamic properties of DNA and RNA. Accurate knowledge of the CSA becomes particularly important at high magnetic fields, prerequisite for adequate spectral resolution in larger oligonucleotides. Measurement of 13C relaxation rates of protonated carbons in the bases of the so-called Dickerson dodecamer, d(CGCGAATTCGCG)2, at 500 and 800 MHz 1H frequency, together with the previously characterized structure and diffusion tensor yields CSA values for C5 in C, C6 in C and T, C8 in A and G, and C2 in A that are closest to values previously reported on the basis of solid-state FIREMAT NMR measurements, and mostly larger than values obtained by in vacuo DFT calculations. Owing to the noncollinearity of dipolar and CSA interactions, interpretation of the NMR relaxation rates is particularly sensitive to anisotropy of rotational diffusion, and use of isotropic diffusion models can result in considerable errors. Copyright 2006 John Wiley & Sons, Ltd. [source]

Liposome/water lipophilicity: Methods, information content, and pharmaceutical applications

Georgette Plemper van Balen
Abstract This review discusses liposome/water lipophilicity in terms of the structure of liposomes, experimental methods, and information content. In a first part, the structural properties of the hydrophobic core and polar surface of liposomes are examined in the light of potential interactions with solute molecules. Particular emphasis is placed on the physicochemical properties of polar headgroups of lipids in liposomes. A second part is dedicated to three useful methods to study liposome/water partitioning, namely potentiometry, equilibrium dialysis, and 1H-NMR relaxation rates. In each case, the principle and limitations of the method are discussed. The next part presents the structural information encoded in liposome/water lipophilicity, in other words the solutes' structural and physicochemical properties that determine their behavior and hence their partitioning in such systems. This presentation is based on a comparison between isotropic (i.e., solvent/water) and anisotropic (e.g., liposome/water) systems. An important factor to be considered is whether the anisotropic lipid phase is ionized or not. Three examples taken from the authors' laboratories are discussed to illustrate the factors or combinations thereof that govern liposome/water lipophilicity, namely (a) hydrophobic interactions alone, (b) hydrophobic and polar interactions, and (c) conformational effects plus hydrophobic and ionic interactions. The next part presents two studies taken from the field of QSAR to exemplify the use of liposome/water lipophilicity in structure,disposition and structure,activity relationships. In the conclusion, we summarize the interests and limitations of this technology and point to promising developments. 2004 Wiley Periodicals, Inc. Med Res Rev, 24, No. 3, 299,324, 2004 [source]

Modified Microperoxidases Exhibit Different Reactivity Towards Phenolic Substrates

CHEMBIOCHEM, Issue 12 2004
Corrado Dallacosta Dr.
Abstract The reactivity of several microperoxidase derivatives with different distal-site environments has been studied. The distal-site environments of these heme peptides include a positively charged one, an uncharged environment, two bulky and doubly or triply positively charged ones, and one containing aromatic apolar residues. The reactivity in the catalytic oxidation of two representative phenols, carrying opposite charges, by hydrogen peroxide has been investigated. This allows the determination of the binding constants and of the electron-transfer rate from the phenol to the catalyst in the substrate/microperoxidase complex. The electron-transfer rates scarcely depend on the redox and charge properties of the phenol, but depend strongly on the microperoxidase. Information on the disposition of the substrate in the adducts with the microperoxidases has been obtained through determination of the paramagnetic contribution to the1H NMR relaxation rates of the protons of the bound substrates. The data show that the electron-transfer rate drops when the substrate binds too far away from the iron and that the phenols bind to microperoxidases at similar distances to those observed with peroxidases. While the reaction rate of microperoxidases with peroxide is significantly smaller than that of the enzymes, the efficiency in the one-electron oxidation of phenolic substrates is almost comparable. Interestingly, the oxyferryl form of the triply positively charged microperoxidases shows a reactivity larger than that exhibited by horseradish peroxidase. [source]