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The purpose of this study was to test the hypothesis that chemical-shift magnetic resonance (MR) imaging may be used to map the distribution of acetic acid during percutaneous chemical ablation procedures. Chemical-shift MR imaging was performed with use of standard methods on a 1.5-T scanner. Phantom and ex-vivo data demonstrated focal increases in the observed signal in chemical-shift MR imaging that correlate well with the site of injection. Preliminary study in a patient with hepatoma revealed focal signal at the injection site. These preliminary results suggest that chemical-shift MR imaging may be used to visualize acetic acid distribution during percutaneous chemical ablation procedures. [ABSTRACT FROM AUTHOR]

Methanogenesis is an anaerobic metabolism responsible for the generation of >90% of the methane formed on Earth today, with important implications for fuels production and global warming. Although methanogenic Archaea have been cultured for over 70 years, key insights regarding electron flow and energy conservation in methanogenesis have only recently emerged. Fundamental differences between two metabolic types of methanogenesis, hydrogenotrophic and methylotrophic, are now understood, with implications for metabolic versatility and the potential for engineering of methanogens to utilize new substrates. The development of model species with genetic and bioinformatic tools has advanced the field and holds potential for further characterizing and engineering of methanogenesis. Our understanding of a related pathway, anaerobic methane oxidation, is in its infancy. [ABSTRACT FROM AUTHOR]

Rationale and Objectives: Physiological noise in blood oxygen level–dependent functional magnetic resonance imaging (BOLD fMRI) has been shown to have characteristics similar to the BOLD signal itself, suggesting that it may have a vascular dependence. In this study, we evaluated the influence of physiological noise in fMRI as revealed by the differences in vasculature sensitivity of gradient-echo echo-planar imaging (GE-EPI) and spin-echo EPI (SE-EPI). Materials and Methods: The contribution of physiological noise to the fMRI signal during activation of the visual cortex was assessed by comparing its temporal characteristics with respect to echo time (TE), using both GE-EPI and SE-EPI. The correlation of the noise in fMRI with apparent diffusion coefficient (ADC) and the number of components required to describe its variance, as determined by principal-component analysis (PCA), were also assessed. Results: The SE-EPI data were less affected by a TE-dependence of noise, in contrast to the apparent physiological noise in GE-EPI. Voxel-wise analysis revealed that total apparent noise increased as ADC values increased, and the relationship was different for GE-EPI and SE-EPI. PCA revealed that while the number of components characterizing the noise in SE-EPI data increased in a TE-dependent manner, approaching that of white noise at long echo time, the number of components from GE-EPI data was TE-independent. Conclusions: The difference in sensitivities to physiological noise between SE-EPI and GE-EPI suggests that extravascular BOLD processes around draining veins contribute significantly to physiological noise in BOLD fMRI, and the suppression of this noise component may enhance SE-EPI BOLD sensitivity at higher fields. [Copyright &y& Elsevier]

: Rationale and ObjectivesThe purpose of this study was (a) to demonstrate the feasibility of computing T1ρ maps of, and T1ρ dispersion in, human wrist cartilage at MR imaging in vivo and (b) to compare T1ρ and T2 weighting in terms of magnitude of relaxation times and signal intensity contrast.: Materials and MethodsT2 and T1ρ magnetic resonance images of wrist joints in healthy volunteers (n = 5) were obtained with a spin-echo sequence and a fast spin-echo sequence pre-encoded with a spin-lock pulse cluster. A 1.5-T clinical imager was used (Signa; GE Medical Systems, Milwaukee, Wis) with a 9.5-cm-diameter transmit-receive quadrature birdcage coil tuned to 63.75 MHz.: ResultsT1ρ relaxation times at a spin-lock frequency of 500 Hz vary from 40.5 msec ± 0.85 to 56.6 msec ± 4.83, and T2 relaxation times vary from 28.1 msec ± 1.88 to 34.5 msec ± 2.63 (mean ± standard error of the mean, n = 5, P < .016) in various regions of the wrist. T1ρ dispersion was observed in the range of spin-lock frequencies studied. T1ρ-weighted images not only have higher signal-to-noise ratios but also show better fluid and fat signal suppression than T2-weighted images.: ConclusionIt was possible to perform T2- and T1ρ-weighted MR imaging of human wrist cartilage in vivo with standard clinical imagers. The higher signal-to-noise ratio and improved contrast between cartilage and surrounding fat achieved with T1ρ imaging may provide better definition of lesions and accurate quantitation of small changes in cartilage degeneration. [Copyright &y& Elsevier]

The methanogenic archaean Methanococcus maripaludis can use ammonia, alanine, or dinitrogen as a nitrogen source for growth. The euryarchaeal nitrogen repressor NrpR controls the expression of the nif (nitrogen fixation) operon, resulting in full repression with ammonia, intermediate repression with alanine, and derepression with dinitrogen. NrpR binds to two tandem operators in the nif promoter region, nifOR1 and nifOR2. Here we have undertaken both in vivo and in vitro approaches to study the way in which NrpR, nifOR1, nifOR2, and the effector 2-oxoglutarate (2OG) combine to regulate nif expression, leading to a comprehensive understanding of this archaeal regulatory system. We show that NrpR binds as a dimer to nifOR1 and cooperatively as two dimers to both operators. Cooperative binding occurs only with both operators present, nifOR1 has stronger binding and by itself can mediate the repression of nif transcription during growth on ammonia, unlike the weakly binding nifOR2. However, nifOR2 in combination with nifOR1 is critical for intermediate repression during growth on alanine. Accordingly, NrpR binds to both operators together with higher affinity than to nifOR1 alone. NrpR responds directly to 2OG, which weakens its binding to the operators. Hence, 2OG is an intracellular indicator of nitrogen deficiency and acts as an inducer of nif transcription via NrpR. This model is upheld by the recent finding (J. A. Dodsworth and J. A. Leigh, submitted for publication) in our laboratory that 2OG levels in M. maripaludis vary with growth on different nitrogen sources. [ABSTRACT FROM AUTHOR]

Summary: Plants and microorganisms reduce environmental inorganic nitrogen to ammonium, which then enters various metabolic pathways solely via conversion of 2-oxoglutarate (2OG) to glutamate and glutamine. Cellular 2OG concentrations increase during nitrogen starvation. We recently identified a family of 2OG-sensing proteins—the nitrogen regulatory protein NrpR—that bind DNA and repress transcription of nitrogen assimilation genes. We used X-ray crystallography to determine the structure of NrpR regulatory domain. We identified the NrpR 2OG-binding cleft and show that residues predicted to interact directly with 2OG are conserved among diverse classes of 2OG-binding proteins. We show that high levels of 2OG inhibit NrpRs ability to bind DNA. Electron microscopy analyses document that NrpR adopts different quaternary structures in its inhibited 2OG-bound state compared with its active apo state. Our results indicate that upon 2OG release, NrpR repositions its DNA-binding domains correctly for optimal interaction with DNA thereby enabling gene repression. [ABSTRACT FROM AUTHOR]