Laurel O. Sillerud

Transformation of selenate and selenite to elemental selenium byDesulfovibrio desulfuricans

SummaryDesulfovibrio desulfuricans (DSM 1924) can be adapted to grow in the presence of 10 mM selenate or 0.1 mM selenite. This growth occurred in media containing formate as the electron donor and either fumarate or sulfate as the electron acceptor. As determined by electron microscopy with energy-dispersive X-ray analysis, selenate and selenite were reduced to elemental selenium which accumulated inside the cells. Selenium granules resulting from selenite metabolism were cytoplasmic while granules of selenium resulting from selenate reduction appeared to be in the periplasmic region. The accumulation of red elemental selenium in the media following stationary phase resulted from cell lysis with the liberation of selenium granules. Growth did not occur with either selenate or selenite as the electron acceptor and13C nuclear magnetic resonance indicated that neither selenium oxyanion interfered with fumarate respiration. At 1 μM selenate and 100 μM selenite, reduction byD. desulfuricans was 95% and 97%, respectively. The high level of total selenate and selenite reduced indicated the suitability ofD. desulfuricans for selenium detoxification.

Pulsed-gradient spin-echo diffusion studies in NMR imaging. Effects of the imaging gradients on the determination of diffusion coefficients

Studies of self-diffusion by magnetic resonance imaging using variations of the pulsed-gradient spin-echo experiment are complicated by the presence of the imaging-gradient pulses. This problem is particularly severe in NMR microscopy, where the diffusion gradients are of the same order or even smaller than the imaging gradients. Due to cross terms between the diffusion gradient and parallel imaging gradients, the Stejskal-Tanner relation no longer applies. This commonly used equation could result in significant overestimation of the self-diffusion coefficient when used in such instances. The effect of diffusion on signal attenuation in a number of spin-echo diffusion imaging sequences has been analyzed, and analytical expressions including the cross terms with the imaging gradients have been derived. The equations derived were verified experimentally through measurements of the self-diffusion coefficient of water, using high-resolution microimaging (imaging gradients of 10–15 G/cm, pixel size of 23 μm) at 400 MHz. Including the cross terms in the data analysis yields values within the literature range (2.6 × 10−5 cm2/s) for the self-diffusion coefficient of water. Neglecting the cross terms is demonstrated to result in a tenfold over-estimation of the diffusion coefficient. When imaging gradients which are larger than the incremented diffusion gradient are used, the experiment becomes significantly more sensitive to diffusion effects, due to the cross terms between the gradients. This predicted and observed result improves the accuracy of imaging diffusion experiments and may also be applicable in spectroscopic diffusion measurements.

A fluorometric study of the interaction of bradykinin with lipids.

The interaction of bradykinin (BK) with lipids has been followed by steady-state fluorescence measurements. Addition of either cerebroside sulfate (CS) or phosphatidylinositol (PI), solubilized with the nonionic surfactant C12E8, to BK or its analogue [Gly6]-BK enhances the relative fluorescence intensity of peptide emission at 288 nm. Fluorometric titration of the peptide with lipid has been used to quantitate the interactions in terms of stoichiometry and equilibrium constant. Jobs method of continuous variation for the BK-CS interaction gave a stoichiometry of 1:2 for the complex. The value of the equilibrium constant, K, for the interaction of either BK or [Gly6]-BK with CS is 1.5.10(4) M-1. The BK-PI interaction is weaker; K = 5.0.10(3) M-1. Although electrostatic forces no doubt play a major role in these interactions, measurements on the model peptide Gly-Phe-Gly indicate that the phenylalanine residues of BK are disposed in the hydrophobic environment provided by the lipid-C12E8 mixed micelle. 13C-NMR measurements on [99% 13C alpha-Gly6]-BK show that there is no change in its cis/trans ratio upon interaction with CS. The increase in the relative fluorescence intensity of BK accompanying its cooperative interaction with sodium dodecyl sulfate (SDS) implicates the role of hydrophobic forces in this interaction as well. These results bear on the interpretation of the changes in circular dichroism (CD) of BK caused by SDS.

Transverse relaxation time constraints on resolution in one-dimensional, phase- and frequency-encoded nuclear magnetic resonance imaging☆

Abstract The theoretical dependence of the resolution on the relationship of sampling time to transverse relaxation time ( T 2 ) for frequency-encoded, one-dimensional NMR imaging using constant field gradients has been investigated. A resolution function that is explicitly dependent on the sampling time is derived, and it is shown that the observed image of an object can be written as a convolution of the sample magnetization with this resolution function. This function is explicitly calculated for two cases of interest: (1) for sampling times much shorter than T 2 , and (2) for sampling times much longer than T 2 . These cases are illustrated for two examples: (1) a uniform magnetic bar, and (2) uniform periodic magnetic bars. When oscillating gradients are utilized, these results still hold in the limit of slow oscillation. The resolution in phase-encoded NMR imaging is not explicitly dependent on the sampling time.

6 – NMR Microscopy

Publisher Summary Nuclear magnetic resonance (NMR) microscopy refers to the generation of NMR images with micrometer-scale resolution within the pixel plane. As a method for noninvasive three-dimensional microscopy, it has an advantage over light microscopy in opaque dielectric samples and in obtaining information beyond the 500-nm limit of confocal microscopy. At this resolution, NMR microscopy does not directly compete with other microscopy methods for the elucidation of tissue structure; instead, it is sensitive to the details of molecular structure, chemical dynamics, and intermediary metabolism. NMR spectroscopy has been successful with respect to the elucidation of chemical structure and metabolism. It can give spatial information about these chemical and dynamic events. NMR microscopy is noninvasive and nondestructive, as long as the samples fit within the confines of the receiver coils. There are no known significant biological effects of the low-frequency electromagnetic fields used in the generation of NMR images. NMR microscopy is well suited to the examination of biological samples under physiological conditions of temperature, pH, ionic strength, and atmospheric pressure. These attributes of NMR have led to the explosive growth in the use of NMR imaging in medicine.

13C and 31P NMR Studies of Prostate Tumor Metabolism

In 1989 an estimated 104,000 cases of prostatic adenocarcinoma will account for about 20% of all male cancers and 11% of all male cancer-related deaths in the U.S.A. As the U.S. population ages, the incidence of this specific tumor type, which is most common in males over 50 years of age, will increase substantially. Prostatic cancers display widely-varying growth rates which impact on the prognosis and required therapeutic intervention. Histologic examination of tumor types is widely used to correlate morphology with growth rates, but there are still histologically-similar tumors which vary markedly in growth characteristics. Neoplasia differs from normal cellular growth in the expression of one or more genes, a feature of cancer which can result in an altered metabolism of tumor cells. We are using Nuclear Magnetic Resonance Spectroscopy (NMRS), a non-invasive and non-destructive method for observing metabolic events both in vitro and in vivo (1–22), to elucidate these metabolic alterations in prostate tumors with the goal of improving our basic understanding of the oncogenetic process in this organ.

Synthesis of l-(4-2H)erythrose, l-)1-13C, 5-2H)arabinose and l-(2-13C, 5-2H)arabinose and identification of the intermediates by 2H and 13C-N.M.R. spectroscopy☆

Abstract l -(1- 13 C, 5- 2 H)Arabinose ( 6 D) and l -(2- 13 C, 5- 2 H)arabinose ( 8 D) have been synthesized by degradation of 2,3- O -isopropylidene-α- l -rhamnofuranose ( 2 ) to l -(4- 2 H)erythrose ( 5β , 5α D), with subsequent chain elongation to 6 D plus l -(1- 13 C, 5- 2 H)ribose ( 7 D), the latter being converted into 8 D. Intermediates were identified by complete assignment of the 13 C chemical shifts employing carbon-carbon and carbon-deuterium coupling constants, deuteration shifts, differential isotope-shifts, and deuterium spectra. The anomeric carbon atoms of 2 and 2,3- O -isopropylidene- l -(1- 2 H) erythrose ( 4 D) gave only single 13 C resonances, suggesting that these two compounds exists in only one major anomeric configuration, clarifying previously reported work. The synthesis of 2,3- O -isopropylidene- l -(1- 2 H)rhmanitol ( 3 D) facilitated the assignment of the signals in the 13 C spectra of the nondeuterated analog. Specific deuterium-enrichment and the observed carbon-deuterium coupling ( 1 J C,D ∼22 Hz) not only served to identify the deuterated carbon atom unambiguously in 3 but also permitted assignment of closely spaced resonances. The deuterium spectrum of 2,3- O -isopropylidene- l -(1- 2 H)erythrofuranose ( 4 D) showed only a single resonance, indicating preponderance of one anomer, in accord with the observation of a single C-1 resonance in the 13 C spectrum.

Waste-Management Education and Research Consortium (WERC) annual progress report, 1991--1992

This report contains the following appendices: Appendix A - Requirements for Undergraduate Level; Appendix B - Requirements for Graduate Level; Appendix C - Graduate Degree In Environmental Engineering; Appendix D - Non-degree Certificate Program; Appendix E - Curriculum for Associate Degree Program; Appendix F - Curriculum for NCC Program; Appendix G - Information 1991 Teleconference Series; Appendix H - Information on 1992 Teleconference Series; Appendix I - WERC interactive Television Courses; Appendix J - WERC Research Seminar Series; Appendix K - Sites for Hazardous/Radioactive Waste Management Series; Appendix L- Summary of Technology Development of the Second Year; Appendix M - List of Major Publications Resulting from WERC; Appendix N - Types of Equipment at WERC Laboratories.