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Biomedical subjects

T A Cross

Publications and source records attributed to T A Cross.

83 records · Page 5Linked to original sources
PubMed1984

Ketogenesis in the living rat followed by 13C NMR spectroscopy.

The metabolic fate of 13C1-labeled butyrate in the liver of living rats has been studied by 13C NMR. The formation of the ketone bodies acetoacetate and beta-hydroxybutyrate was observed in vivo as well as resonances from glutamate, glutamine, and carbonate. The observed time course of these metabolites demonstrates the potential of the technique to measure enzyme kinetics in vivo and also to measure the enzyme capacity of a given organ to metabolize a substrate. The in vivo spectra were compared to in vitro spectra of the excised liver and perchloric acid extracts of the liver. Observation of the metabolites and monitoring of their time course in vivo would not have been possible without distinct improvements in the spectral resolution and the spatial localization of the radio-frequency field within the liver. As a novel approach, we have selected the carbonyl region of the 13C NMR spectra for identifying the ketone bodies and other oxidation products in the liver.

3-Hydroxybutyric Acid↗
PubMed1983

31P nuclear magnetic resonance of the RNA in tobacco mosaic virus.

Solid state 31P n.m.r. data concerning the structure of the RNA in TMV are presented in light of the prior diffraction and model building results on this system (Stubbs et al., 1977; Stubbs & Stauffacher, 1981). The 31P chemical shift anisotropy powder pattern of a stationary, unoriented solution of TMV shows the RNA to be immobilized by the coat protein-RNA interactions, since the principal values (sigma 11 = 83, sigma 22 = 25, sigma 33 = -108 p.p.m. relative to external 85% H3PO4) are essentially the same as those of a static phosphodiester group. There are three peaks in the isotropic 31P n.m.r. spectrum obtained with magic angle sample spinning, indicating three distinct phosphate environments. There are three peaks in the 31P n.m.r. spectrum from an oriented TMV solution, indicating three distinct phosphate orientations.

Magnetic Resonance Spectroscopy↗
PubMed1983

Comparison of protein and deoxyribonucleic acid backbone structures in fd and Pf1 bacteriophages.

The conformations of the protein and nucleic acid backbones in the filamentous viruses fd and Pf1 are characterized by one- and two-dimensional solid-state NMR experiments on oriented virus solutions. Striking differences are observed between fd and Pf1 in both their protein and DNA structures. The coat proteins of fd and Pf1 are almost entirely alpha helical and in both viruses most of the helix is oriented parallel to the filament axis. fd coat protein is one stretch of alpha helix that is slightly slued about the filament axis. In Pf1 coat protein two distinct sections of alpha helix are present, the smaller of which is tilted with respect to the filament axis by about 20 degrees. The DNA backbone structure of fd is completely disordered. By contrast, the DNA backbone of Pf1 is uniformly oriented such that all of the phosphodiester groups have the O-P-O plane of the nonesterified oxygens approximately perpendicular to the filament axis.

Bacteriophages↗
PubMed1982

Protein dynamics by solid-state NMR: aromatic rings of the coat protein in fd bacteriophage.

The motions of the aromatic amino acids of the fd bacteriophage coat protein are described by solid-state 2H, 13C, and 15N NMR. Tryptophan-26 is immobile on time scales as slow as 10(3) HZ. The phenylalanine and tyrosine rings undergo 180 degree flips about the C beta--C gamma bond axis more often than 10(6) HZ as well as small-amplitude rapid motions in other directions.

Coliphages↗
PubMed1981

Hydrogen-1 and carbon-13 nuclear magnetic resonance of the aromatic residues of fd coat protein.

The aromatic residues of fd coat protein in sodium dodecyl sulfate micelles are characterized by 1H and 13C NMR. Resonances from both types of nuclei show structure-induced chemical shift dispersion and line widths indicative of a folded native structure for the protein. The two tyrosines were found to have pKas of 12.3 and 12.5 by 1H NMR and spectrophotometric titrations. 13C relaxation measurements show that two of the three Phe rings have significant internal mobility, the two Tyr rings have moderate internal mobility, and the Trp side chain is completely immobilized. Qualitative comparisons are made between the intact virus and the isolated coat protein.

Amino Acid Sequence↗
PubMed1981

Structure and architecture of the bacterial virus fd. An infrared linear dichroism study.

Oriented gels of intact bacterial virus fd have been invetigated by infrared linear dichroism. Infrared absorption band maxima and dichroism indicate an alpha-helix content of the major coat protein of 95-100%. The alpha-helical rods of the coat protein are aligned parallel to the long axis of the virion with an inclination roughly estimated to approximately 37 degree. The presence of DNA infrared bands at 968, 885, 830 and 799 cm-1, the absence of a band at 860 cm-1 and the perpendicular polarization of the symmetric PO-2 stretching vibration at 1085 cm-1 are all indicative of a B-type backbone conformation in the single-stranded DNA. We find no evidence for specific interaction between aromatic side groups (phenylalanine, tyrosine) and the DNA bases. Our results independently confirm most features of the model of Marvin and co-workers [2,15 ] based on low-resolution X-ray diffraction studies. However, our findings contradict their suggestion of an A-type DNA in the bacterial virus fd. Two results are consistent with rigid and stable order in the virus. First, over a 4-day period, 65% of the peptide hydrogens remain unexchanged with deuterium. Second, changes in the relative humidity of the sample do not result in any shifts in the DNA spectrum that are characteristic of free DNA.

Coliphages↗
PubMed1980

Nuclear magnetic resonance of the filamentous bacteriophage fd.

The filamentous bacteriophage fd and its major coat protein are being studied by nuclear magnetic resonance (NMR) spectroscopy. 31P NMR shows that the chemical shielding tensor of the DNA phosphates of fd in solution is only slightly reduced in magnitude by motional averaging, indicating that DNA-protein interactions substantially immobilize the DNA packaged in the virus. There is no evidence of chemical interactions between the DNA backbone and the coat protein, since experiments on solid virus show the 31P resonances to have the same principle elements of its chemical shielding tensor as DNA. 1H and 13C NMR spectra of fd virus in solution indicate that the coat proteins are held rigidly in the structure except for some aliphatic side chains that undergo relatively rapid rotations. The presence of limited mobility in the viral coat proteins is substantiated by finding large quadrupole splittings in 2H NMR of deuterium labeled virions. The structure of the coat protein in a lipid environment differs significantly from that found for the assembled virus. Data from 1H and 13C NMR chemical shifts, amide proton exchange rates, and 13C relaxation measurements show that the coat protein in sodium dodecyl sulfate micelles has a native folded structure that varies from that of a typical globular protein or the coat protein in the virus by having a partially flexible backbone and some rapidly rotating aromatic rings.

Bacterial Proteins↗
PubMed1979

NMR of fd coat protein.

The conformations of the major coat protein of a filamentous bacteriophage can be described by nuclear magnetic resonance spectroscopy of the protein and the virus. The NMR experiments involve detection of the 13C and 1H nuclei of the coat protein. Both the 13C and 1H nuclear magnetic resonance (NMR) spectra show that regions of the polypeptide chain have substantially more motion than a typical globular protein. The fd coat protein was purified by gel chromatography of the SDA solubilized virus. Natural abundance 13C NMR spectra at 38 MHz resolve all of the nonprotonated aromatic carbons from the three phenylalanines, two tyrosines, and one tryptophan of the coat protein. The alpha carbons of the coat protein show at least two different classes of relaxation behavior, indicative of substantial variation in the motion of the backbone carbons in contrast to the rigidity of the alpha carbons of globular proteins. The 1H spectrum at 360 MHz shows all of the aromatic carbons and many of the amide protons. Titration of a 1H spectra gives the pKas for the tyrosines.

Amino Acid Sequence↗