Bayesian signal extraction from noisy FT NMR spectra

Summary The statistical interpretation of the histogram representation of NMR spectra is described, leading to an estimation of the probability density function of the noise. The white-noise and Gaussian hypotheses are discussed, and a new estimator of the noise standard deviation is derived from the histogram strategy. The Bayesian approach to NMR signal detection is presented. This approach homogeneously combines prior knowledge, obtained from the histogram strategy, together with the posterior information resulting from the test of presence of a set of reference shapes in the neighbourhood of each data point. This scheme leads to a new strategy in the local detection of NMR signals in 2D and 3D spectra, which is illustrated by a complete peak-picking algorithm.     

Neutralization of radiation damping by selective feedback on a 400 MHz NMR spectrometer

Summary Radiation damping is a phenomenon well known among NMR spectroscopists of proteins as a source of undesirable features, especially in high-field and high-Q probe NMR. In this paper, we present an electronic neutralization network which dramatically reduces radiation damping. It detects the radiation field profile and feeds back into the probe an rf field with identical amplitude and opposite phase. Experimental results of a practical implementation carried out on a 400 MHz Bruker spectrometer are shown.     

Keep all the pieces: Systematics 2000 and world conservation

Conserving biological diversity requires a major effort in conducting survey and inventories, establishing priorities, selecting protected areas, managing resources and monitoring the effects of management. Systematics has an important contribution to make to each of these five major activities. Further, the new Convention on Biological Diversity requires systematics information to support action under virtually all of its substantive conservation and sustainable use articles. It seems apparent that large reference collections contribute directly to development, and development assistance agencies should recognize that investing in maintaining these collections is a legitimate form of development assistance.     

C nuclear magnetic resonance studies of the binding of alkyl isocyanides to soybean leghemoglobin; comparison with animal myoglobins

¹³C NMR of labelled alkyl isocyanide ligands has been used with a view to probe the protein environment around the heme site of Soybean leghemoglobin, and comparatively, those of sperm whale myoglobin and monomeric Glycera hemoglobin. The terminal carbon of the isocyanide, which is known to be highly sensitive to change in hybridization of the nitrogen, could be expected to reflect the movement of the alkyl group through steric interactions. Three alkyl isocyanides (alkyl = methyl, ethyl & n-butyl) have therefore been used and the ¹³C° chemical shift values were measured for each ligand bound to the various proteins studied.In all cases, the ¹³C° resonances of the bound ligand were shifted considerably downfield with respect to those of the free unbound species, but the pattern of these displacements revealed more pronounced steric hindrance in the case of some proteins compared to others. The modifications of the chemical shift values on binding Δδ = δ_bound — δ_free) were least in the case of leghemoglobin; moreover, the Δδ values were insensitive to the length of the alkyl chain (methyl to n-butyl) when bound to leghemoglobin, in contrast to the other proteins examined. The results are interpreted as arising from a diminished steric hindrance to isocyanide binding with leghemoglobin, in conformity with the recently published X-ray structure which reports the existence of a large heme pocket on the distal side.     

Changes in 32P-phosphorus compounds during translocation in Laminaria digitata (L.) lamouroux

³²P was applied to a Laminaria digitata thallus and the pattern of ³²P phosphorylated compounds was studied, as a function of time, in the different tissues involved in translocation, i.e. source, pathway and sinks. The results showed that, 3 hours after absorption by the uptake region (lamina), the bulk of the radioactivity was incorporated into organic compounds (70 to 80% of total ³²P taken up), hexose monophosphates being the heaviest labelled. Further change in that region was marked by an accumulation of ³²P in the inorganic pool (65 to 70% after 13 days). Conversely, the ³²P pattern in the medulla of the stipe, which initially showed a similar pattern to the uptake region, did not vary during translocation. The pattern of ³²P distribution into sinks (growing stipe peripheral tissue or hapteron) leads to accumulation of the radioactive element in inorganic and acid-insoluble fractions. These results are discussed in terms of comparative distribution of ³²P in the different parts of the thallus and suggest that phosphate moves as Pi in that alga.Abbreviations TCA trichloroacetic acid - Po organic phosphate - Po sol acid-soluble organic phosphate fraction - Po insol acidinsoluble organic phosphate fraction - Pi morganic phosphate fraction - P lip lipidic phosphate - Np protein nitrogen - ATP adenosine triphosphate - ADP adenosine diphosphate - PEP phosphoenolpyruvic acid - PGA phosphoglyceric acid - G-1-P glucose-1-phosphate - G-6-P glucose-6-phosphate - UDPG uridine diphosphoglucose     

Differentiation under the control of insulin of rat preadipocytes in primary culture: Isolation of homogeneous cellular fractions by gradient centrifugation

Using a density gradient medium (Percoll) we succeeded in isolating homogeneous cell populations from the stromal-vascular fraction of the inguinal tissue of 3-day-old rats. In primary culture, in medium 199 supplemented with 10% fetal calf serum and 5.5 mM glucose, almost complete differentiation (90%) of these fractions was obtained for the first time in presence of a physiological concentration of insulin (10^?9 M). During the adipose conversion, insulin markedly enhanced the activities of glycerol-3-phosphate dehydrogenase and acid:CoA ligase. When VLDL and heparin were added with insulin to the medium, this effect was not potentiated. On the contrary, VLDL and heparin in presence of insulin increased the triglyceride content of the cells. With VLDL and heparin only, the biochemical and morphological characteristics of the cells were very similar to those observed in control culture. The heavier fraction was morphologically heterogeneous and did not undergo the adipose conversion to the same extent as the two lighter fractions. It was concluded that this model could be helpful in studying the proliferation and the differentiation of preadipocytes at an early stage of development.