Biomedical subjects

T J Norwood

Publications and source records attributed to T J Norwood.

10 recordsLinked to original sources

PubMed2000

In-phase selective excitation of overlapping multiplets.

An editing experiment is presented that selects for a peak on the basis of its chemical shift and that of one of its scalar coupling partners. The selected multiplet is pure in-phase. The editing procedure can be used in conjunction with 1D TOCSY/HOHAHA and NOE measurements. The pulse sequence described is particularly suitable for small molecules; data is presented for Gramicidin S and dehydrotestosterone.

Magnetic Resonance Spectroscopy↗

PubMed2000

Overall rotational diffusion and internal mobility in domain II of protein G from Streptococcus determined from 15N relaxation data.

The backbone dynamics and overall tumbling of protein G have been investigated using 15N relaxation. Comparison of measured R2/R1 relaxation rate ratios with known three-dimensional coordinates of the protein show that the rotational diffusion tensor is significantly asymmetric, exhibiting a prolate axial symmetry. Extensive Monte Carlo simulations have been used to estimate the uncertainty due to experimental error in the relaxation rates to be D(parallel)/D(perpendicular) = 1.68 +/- 0.08, while the dispersion in the NMR ensemble leads to a variation of D(parallel)/D(perpendicular) = 1.65 +/- 0.03. Incorporation of this tensorial description into a Lipari-Szabo type analysis of internal motion has allowed us to accurately describe the local dynamics of the molecule. This analysis differs from an earlier study where the overall rotational diffusion was described by a spherical top. In this previous analysis, exchange parameters were fitted to many of the residues in the alpha helix. This was interpreted as reflecting a small motion of the alpha helix with respect to the beta sheet. We propose that the differential relaxation properties of this helix compared to the beta sheet are due to the near-orthogonality of the NH vectors in the two structural motifs with respect to the unique axis of the diffusion tensor. Our analysis shows that when anisotropic rotational diffusion is taken into account NH vectors in these structural motifs appear to be equally rigid. This study underlines the importance of a correct description of the rotational diffusion tensor if internal motion is to be accurately investigated.

Bacterial Proteins↗

PubMed1999

Quantitative measurement of long range nuclear Overhauser enhancement.

Measurement of nuclear Overhauser enhancement is one of the mainstays of structural studies of molecules in solution. Measurements, particularly over long distances, are often compromised by spin diffusion. A robust and accurate method for measuring nuclear Overhauser enhancements that are largely free of spin diffusion effects is presented. The effects of using imperfect radiofrequency pulses are considered and experimental data are presented for Amphotericin B.

Magnetic Resonance Spectroscopy↗

PubMed1999

Protein-ligand interactions measured by 15N-filtered diffusion experiments.

NMR diffusion coefficient measurements have been shown to be sensitive to the conformational and oligomeric states of proteins. Recently, heteronuclear-filtered diffusion experiments have been proposed [Dingley et al. (1997) J. Biomol. NMR, 10, 1-8]. Several new heteronuclear-filtered diffusion pulse sequences are proposed which are shown to have superior sensitivity to those previously proposed. One of these new heteronuclear-filtered diffusion experiments has been used to study the binding of an SH3 domain to a peptide. Using this system, we show that it is possible to measure binding constants from diffusion coefficient measurements.

Diffusion↗

PubMed1998

Spectral editing technique for the in vitro and in vivo detection of taurine.

In vivo 1H NMR spectroscopy has proven to be a useful noninvasive tool for the investigation of numerous metabolic and physiological states. Taurine is potentially a useful indicator in neonate development and is involved in a number of physiological processes. However, it could not previously be observed in the in vivo 1H spectrum because of overlap with adjacent resonances. We have developed a spectral editing technique based upon double quantum filtration which allows the taurine resonances to be resolved from adjacent peaks. The experiment is demonstrated both on perchloric acid rodent brain extract and on rodent brain homogenate.

Algorithms↗

PubMed1998

Practical aspects of the measurement of the diffusion of proteins in aqueous solution.

NMR diffusion measurements have been shown to be a useful tool for investigating the conformation and oligomeric state of proteins. Four main problems associated with making diffusion measurements of proteins in aqueous solution are identified and solutions proposed. The resulting experiment is demonstrated for an aqueous solution of hen egg white lysozyme.

Animals↗

PubMed1993

A new method for diffusion weighted imaging.

A new method for generating diffusion contrast in magnetic resonance imaging is presented. This technique is robust enough to allow implementation on conventional imaging systems without hardware modifications. Results from phantom measurements are reported. Qualitative contrast changes in magnetic resonance images derived from live mammalian brain are also demonstrated.

Animals↗

PubMed1992

Heteronuclear 1H-15N nuclear magnetic resonance studies of the c subunit of the Escherichia coli F1F0 ATP synthase: assignment and secondary structure.

Nuclear magnetic resonance (NMR) studies of the c subunit of F1F0 ATP synthase from Escherichia coli are presented. A combination of homonuclear (1H-1H) and heteronuclear (1H-15N) 2D and 3D methods was applied to the 79-residue protein, dissolved in trifluoroethanol. Resonance assignment for all the backbone amide groups and many C alpha H side-chain protons was achieved. Analysis of inter- and intraresidue 1H-1H nuclear Overhauser effect (NOE) data and scalar coupling constant information indicates that this protein contains two extended regions of predominant alpha-helical character (residues 10-40 and 48-77) separated by an eight-residue segment which displays little evidence of ordered secondary structure. This model is consistent with information about the molecular motion of the protein deduced from 15N-1H heteronuclear NOE data and observed pKa values of carboxylic acid groups.

Amino Acid Sequence↗

PubMed1989

Improved resolution in 1H-detected 1H-15N correlation experiments.

The determination of protein structure by NMR is restricted at molecular masses above 10 kDa by overlapping resonances. One way of overcoming this problem is to label the protein with 15N. The conventional way to record 15N spectra is to use heteronuclear multiple-quantum coherence. We present here an alternative approach based on 15N single-quantum coherence. This is shown to have substantial advantages over the multiple-quantum method, including better F1 resolution.

Escherichia coli↗

PubMed1989

Spectral editing techniques for 31P NMR spectroscopy of blood.

Although the measurement of the pH of biological systems using the 31P NMR response of inorganic phosphate is well known, sometimes in blood absolute determination of the intensity and position of the Pi resonance is precluded by overlap from the doublet resonance of 2,3-diphosphoglycerate. Three techniques which overcome this problem by eliminating the doublet are described and their sensitivity to the experimental parameters is assessed.

Blood Chemical Analysis↗