Biomedical subjects
Publications and source records attributed to R G Bryant.
Significant rf noise reduction is demonstrated by enclosing the patient in a conducting cage grounded to the magnet bore in a 22-cm-bore spectrometer system capable of examining magnetic images and spectroscopy of human limbs. This method of noise reduction was found to be reliable, simple, and efficient for dealing with ambient rf noise in an unshielded room.
A single turn solenoid, also called a loop-gap resonator, is a device that is efficient for radio frequency spectroscopy on relatively large samples. Thus, the device provides an effective means for magnetic imaging where the single turn solenoid may serve both as the transmitter and receiver coil. The device is readily constructed and provides very efficient use of radio frequency (RF) power for imaging extremities such as breasts, arms, feet, and hands. The resulting magnetic images are acquired in short times with good anatomical resolution and considerable reduction of the RF power delivered to the patient.
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The differential and selective sodium dodecyl sulfate-polymyxin B-sucrose medium (SPS) of Kitaura et al. (T. Kitaura, S. Doke, I. Azuma, M. Imaida, K. Miyano, K. Harada, and E. Yabuuchii, FEMS Microbiol. Lett. 17:205-209, 1983), which highlights alkylsulfatase activity, was evaluated for its potential use in the direct isolation and enumeration of Vibrio vulnificus from shellfish. V. vulnificus was detected by this method in six of nine shellfish samples collected from diverse geographic locales during the summer of 1986. Direct enumeration of V. vulnificus at 7.0 X 10(2) to 2.2 X 10(4) CFU/g of shellfish was achieved on SPS agar. All sample results were confirmed in parallel examinations by using conventional glucose-salt-Teepol (Shell Oil Co.) broth and alkaline peptone water enrichment with plating onto thiosulfate-citrate-bile salts-sucrose agar. Additionally, alkylsulfatase activity was evaluated in vitro for 97 strains representing 14 Vibrio spp. V. vulnificus and Vibrio cholerae-01 were the only species consistently found to possess this activity. The range of plating efficiencies for random V. vulnificus strains analyzed on SPS was 11 to 74% (mean, 39%). The use of SPS shows great promise for the study of shellfish and other environmental sources for V. vulnificus.
31P-Nuclear magnetic resonance was used to monitor in situ phosphorus containing compounds in mammary tumors after photodynamic therapy, consisting of administration of hematoporphyrin derivative followed by photoradiation of the lesion. A rapid decrease in ATP along with an increase in Pi resonance intensities was observed. The beta-ATP/Pi ratio decreased by 1 hour, dropping in 2 to 8 hours to 0 to 20 percent of that found prior to photoradiation. Disrupted cells and pycnotic nuclei were observed 48 to 72 hours after photoradiation to a depth of approximately 5 mm. Together with previous studies in vitro, reduction in tumor ATP levels appears to be an early biochemical response to photodynamic therapy.
Ion-DNA interactions are discussed and the applied magnetic field strength dependence of water proton spin-lattice relaxation rates is used to study the Mn(II)-DNA interaction both qualitatively and quantitatively. Associations in which the manganese II (Mn(II)) ion is completely immobilized on the DNA are identified as well as a range of associations in which the ion is only partially reorientationally restricted. Quantitative analysis of the strength of the association in which manganese is immobilized is carried out both with and without a counter-ion condensation correction for electrostatic attraction of the mobile ions. From competition experiments with manganese the relative strengths of the interactions of magnesium and calcium with DNA are found to be identical but less than that of manganese with DNA and the affinity of lithium for DNA is found to be slightly higher than that of sodium. The data demonstrate that the reduced mobility of nonsite-bound ions may have a significant effect on DNA-ion binding analyses performed using magnetic resonance and relaxation methods.
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Breast images obtained at 1.5 T using a loop-gap resonator pair as both the excitation and detection device are presented. The efficiency of this approach is high, as judged by the low level of radio frequency (RF) power required to obtain a 90 degree pulse and the uniformity of the RF field within the resonator pair. A modification of the pair geometry provides for reasonable observation of the tissues through the chest wall and laterally to the axillae.
The proton nuclear magnetic relaxation rate, 1/T1, is reported as a function of d5-glycerol concentration for aqueous manganese(II) ion solutions over a range of magnetic field strengths corresponding to proton Larmor frequencies between 0.01 and 38 MHz. The data are analyzed in terms of the Solomon, Bloembergen, and Morgan equations which are found to be sufficient to account for the relaxation data over the field and concentration ranges studied. These data provide a useful reference for the viscosity dependence of manganese(II)-ion-induced magnetic relaxation in aqueous systems and a useful comparison with macromolecule bound manganese(II)-ion-induced relaxation where the theory is less successful.
The magnetic field dependence of the water proton T2 is calculated for aqueous solutions of nitroxides based on a detailed analysis of early T1 measurements on nitroxide solutions made as a function of magnetic field. The results parallel those for T1 closely and, unlike metal systems, the implications for magnetic imaging are similar.
The catalysis by iron of the formation of reactive oxygen species in biological systems has been well documented. In this present study, we have investigated the hypothesis that iron-catalyzed formation of hydroxyl radical (.OH) from superoxide anion radical (O-.2) and H2O2 requires the availability of at least one iron coordination site that is open or occupied by a readily dissociable ligand such as water. This hypothesis was tested by measuring the catalytic activity of 12 different iron chelates using hypoxanthine and xanthine oxidase to generate O-.2. In these same chelates, we also determined the presence or absence of coordinated water by UV-visible spectroscopy and 1H NMR relaxation measurements. Of all chelates tested, only Fe3+ coordinated to diethylenetriamine pentaacetic acid; ethylenediamine di(o-hydroxyphenylacetic acid), phytate, and Desferal lacked coordination water; and only these four complexes failed to produce hydroxyl radical. Separate determinations of the two redox half-reactions involved (i.e. Fe3+ + O-.2----Fe2+ + O2 and Fe2+ + H2O2----Fe3+ + .OH + OH-) indicate that an available coordination site is necessary for the latter (Fenton) reaction. This principle governing iron reactivity may help advance our understanding of the mechanism of oxidative damage in biological systems and may also permit the design of more effective chelators for the control of iron in biological systems.
The 43Ca NMR spectra are reported for solutions of prothrombin fragment 1 in the presence and absence of phospholipid. The calcium NMR spectrum permits distinction between three thermodynamic classes of calcium-binding interactions. The calcium ion in the lipid-free solutions was labile, with maximum residence times estimated for the average protein site in the range of 0.5-1 ms. The calcium spectrum was sensitive to the protein association and the addition of phospholipid, which appears to sharpen the calcium specificity for the protein sites. The calcium NMR spectra in the presence of phospholipid are similar to those in lipid-free solutions, which suggests that the calcium ion remains labile in the lipid-protein complex.
The intensities of regions of interest in saturation-recovery (SR) and inversion-recovery (IR) images obtained with a new magnetic resonance (MR) scanner were compared with theoretically expected results, using phantom materials that had been accurately characterized in a specialized MR spectrometer. The data revealed significant dependence on the spin-spin relaxation time (T2), which was not expected on the basis of a simple model. The cause of this T2 dependence is discussed. The appearance and contrast of certain tissues in IR and SR images may be different than expected on the basis of the simple model. The results indicate that caution is required in making general claims about the efficacy of specific MR techniques because of potential subtle differences in the way that even the most basic sequences are implemented on individual imaging devices.
A review of three "emerging" foodborne pathogen groups is presented, including Campylobacter jejuni/coli, Yersinia enterocolitica, and foodborne Vibrio sp.
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Nuclear magnetic relaxation measurements are reported as a function of field strength corresponding to the frequency range from 0.01 to 20 MHz for water protons in monoclinic lysozyme crystals at 278 and 298 K. Though the instrumentation used selects only a portion of the total magnetization to sample, the data clearly indicate a field dependence of the relaxation rate that signals the presence of slow motions characterized by time constants in the range of tenths of microseconds and slower. The data support, but do not uniquely prove, the hypothesis that this time scale is that appropriate to the isotropic averaging of locally anisotropic water molecule motion at the protein surface.
Deuterium NMR spectra are reported for lysozyme crystals, powders, and frozen solutions. At high water contents the spectrum is a superposition of a narrow central component and a quadrupole doublet. The quadrupole splitting and the relaxation rates of both components, monitored as a function of water content and temperature, are discussed in terms of models for the water-protein interaction. The anisotropy of the water molecule motion is clearly demonstrated by the deuterium quadrupole splitting observed in the protein single crystal, but such splittings were not found in protein powders and frozen protein solutions. We therefore suggest that the most useful view of such data is to consider the water-protein interactions at the surface to be mixed rapidly and that a distribution of interactions be invoked rather than an oversimplified view often taken of a two or n-site mixing where n is small.
The effects of temperature and pH on the solution conformation of native prothrombin fragment 1 were examined with 1H NMR spectroscopy. A calcium-dependent quenching of the intrinsic protein fluorescence was used to monitor calcium binding to fragment 1 as an indicator of functional protein. The native fragment 1 NMR spectrum contained several features indicative of a folded protein: (a) nonequivalent histidyl C-2 resonances at 7.9 and 8.1 ppm, (b) two resonances of nearly equal intensity at 7.26 and 7.32 ppm, and (c) a resonance at -1.04 ppm. Temperature studies showed that thermal unfolding of fragment 1 (even at 80 degrees C) was reversible; however, there was an irreversible inactivation step which occurred subsequent to the unfolding. The basis for this inactivation appeared to include disulfide exchange reactions. On the basis of NMR spectra, fragment 1 retained its conformation from pH 7.0 to pH 11.5. From pH 7.0 to pH 5.0, the protein showed a reversible conformational change, and below pH 5, the protein self-associated. The pH dependence of the chemical shift of the tyrosyl resonances indicated a pKa of approximately 10 for the tyrosyl residues. These data suggest that the tyrosyl residues are accessible to solvent in the native protein.