Publications (4)13.57 Total impact
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Article: 'Chiral compartmentation' in metabolism: Enzyme stereo-specificity yielding evolutionary options.
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ABSTRACT: We introduce the concept of 'chiral compartmentation' in metabolism that emerges from the stereo-specificity of enzymes for their substrate(s). The fully differentiated mammalian erythrocyte has no sub-cellular organelles and yet it displays compartmentation of lactic acid that is generated either by glycolysis or the glyoxalase pathway. A form of 'operational compartmentation' exists, based not on the chemistry of the reactive groups in the molecules but their stereoisomerism. This we call 'chiral compartmentation', and the rationale for its 'natural selection' in the erythrocyte (and presumably in the cytoplasm of other cells) is discussed. Increasing awareness of the presence of d-amino acids in proteins in the otherwise dominant 'l-chiral biosphere', and of the preferential use of one enantiomer of a metabolite versus the other is largely due to recent developments in rapidly-applicable, analytical-chemical methods. We confirmed that the glyoxalase pathway yields d-lactic acid by using nuclear magnetic resonance (NMR) spectroscopy of stretched chiral hydrogels. The activity of the two lactate-producing pathways have been described by numerical integration of simultaneous non-linear differential equations, based on enzyme models like that introduced by Michaelis and Menten in 1913.FEBS letters 05/2013; · 3.54 Impact Factor -
Article: Imaging brain deoxyglucose uptake and metabolism by glucoCEST MRI.
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ABSTRACT: 2-Deoxy-D-glucose (2DG) is a known surrogate molecule that is useful for inferring glucose uptake and metabolism. Although (13)C-labeled 2DG can be detected by nuclear magnetic resonance (NMR), its low sensitivity for detection prohibits imaging to be performed. Using chemical exchange saturation transfer (CEST) as a signal-amplification mechanism, 2DG and the phosphorylated 2DG-6-phosphate (2DG6P) can be indirectly detected in (1)H magnetic resonance imaging (MRI). We showed that the CEST signal changed with 2DG concentration, and was reduced by suppressing cerebral metabolism with increased general anesthetic. The signal changes were not affected by cerebral or plasma pH, and were not correlated with altered cerebral blood flow as demonstrated by hypercapnia; neither were they related to the extracellular glucose amounts as compared with injection of D- and L-glucose. In vivo (31)P NMR revealed similar changes in 2DG6P concentration, suggesting that the CEST signal reflected the rate of glucose assimilation. This method provides a new way to use widely available MRI techniques to image deoxyglucose/glucose uptake and metabolism in vivo without the need for isotopic labeling of the molecules.Journal of Cerebral Blood Flow & Metabolism advance online publication, 15 May 2013; doi:10.1038/jcbfm.2013.79.Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 05/2013; · 5.46 Impact Factor -
Article: Simultaneous estimation of T₁ and the flip angle in hyperpolarized NMR experiments using acquisition at non-regular time intervals.
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ABSTRACT: In NMR spectroscopy of the liquid state T(1) is typically measured using an inversion recovery pulse sequence; but with hyperpolarized spins use is made of a sequence of multiple small radiofrequency (RF) induced nutations, α. Depending on the values of α and τ, the time interval between the pulses, the estimate of T(1) can be artifactually smaller than the real value; so without knowing the value of α the estimate of T(1) can be incorrect. Thus, we propose a method that involves a series of pulses with timing governed by a geometric sequence (or in general, any mathematically specified non-uniformly spaced sequence). This approach enables the simultaneous estimation of both the intrinsic T(1) value and α. The method was successfully applied to obtain T(1)=(44.9 ± 0.3)s and α=(4.0 ± 0.2)° (n=3) for a sample of hyperpolarized (13)C-urea in solution, matching with the inversion recovery pulse sequence estimate of T(1)=44 ± 2s using non-hyperpolarized (13)C-urea in solution.Journal of Magnetic Resonance 06/2012; 222:68-73. · 2.14 Impact Factor -
Article: Insights into hERG K(+) channel structure and function from NMR studies.
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ABSTRACT: The unique gating kinetics of hERG K(+) channels are critical for normal cardiac repolarization, and patients with mutations in hERG have a markedly increased risk of cardiac arrhythmias and sudden cardiac arrest. HERG K(+) channels are also remarkably promiscuous with respect to drug binding, which has been a very significant problem for the pharmaceutical industry. Here, we review the progress that has been made in understanding the structure and function of hERG K(+) channels with a particular focus on nuclear magnetic resonance studies of the domains of the hERG K(+) channel.Biophysics of Structure and Mechanism 05/2012; · 2.44 Impact Factor
