Crystallization of Arthrobacter sp. strain 1C N-(1-D-carboxyethyl)-L-norvaline dehydrogenase and its complex with NAD+

The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres.     

Gasanalyse

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Computable error bounds for pointwise derivatives of a Neumann problem

In this paper we discuss the recovery of derivatives and thecomputation of rigorous and useful upper bounds for the pointwiseerror in the recovered derivatives, for finite element approximationsof the Laplace equation with Neumann boundary conditions, especiallyat points close to or on a smooth, curved boundary. We analyzethe dipole image technique for the case of curved boundaries,and show how to compute reliable recovered derivatives and errorbounds even in the limiting case of points lying on the curvedboundary. Numerical experiments show reasonably tight errorbounds for points both close to and away from a curved boundary.     

Instrumental comparison for the determination of cadmium and lead in calcium supplements and other calcium-rich matrices.

Three brands of Ca supplement, a laboratory-reagent grade CaCO3 and a certified reference material (International Atomic Energy Agency H-5 Animal Bone) wee analysed for Cd and Pb by four different analytical techniques, viz., anodic stripping voltammetry inductively coupled plasma mass spectrometry, flame atomic absorption spectrometry and electrothermal atomic absorption spectrometry. The Pb levels measured by the four techniques in the bone powder were within the certified Pb level in this certified reference material. Similarly, no significant differences [p less than 0.05; analysis of variance (ANOVA)] were observed in samples with Pb concentrations greater than 1 microgram g-1. However, the Pb levels in the laboratory-reagent grade CaCO3 obtained by flame atomic absorption spectrometry (0.79 micrograms g-1) averaged about three times higher than those measured by the other three techniques (i.e., 0.25 micrograms g-1). Although no significant differences (p less than 0.05; ANOVA) in Cd levels were observed within any of the samples (intra-sample variability), the Cd concentration measured in the different Ca supplements (inter-sample variability) varied by three orders of magnitude (ranging from 0.07 to 3.59 micrograms g-1).     

ADP-specific sensors enable universal assay of protein kinase activity

Two molecular sensors that specifically recognize ADP in a background of over 100-fold molar excess of ATP are described. These sensors are nucleic-acid based and comprise a general method for monitoring protein kinase activity. The ADP-aptamer scintillation proximity assay is configured in a single-step, homogeneous format while the allosteric ribozyme (RiboReporter) sensor generates a fluorescent signal upon ADP-dependent ribozyme self-cleavage. Both systems perform well when configured for high-throughput screening and have been used to rediscover a known protein kinase inhibitor in a high-throughput screening format.     

Characterization and optimization of HPIC for on-line preconcentration of trace metals with detection by ICP-mass spectrometry

The objective of this study was to investigate the feasibility of using a commercially available cation-exchange column for trace metal preconcentration. In addition, the advantages of interfacing the column to a highly sensitive element-selective detector were examined. A high-performance ion-chromatograph (HPIC) with a high-pressure pump and valve system was used to aid loading and delivery of the mobile phase. An inductively coupled plasma mass spectrometer combination (ICP-MS) was used as a detection device, with interfacing by means of a small diameter liquid-transport tube. The performance of the HPIC/ICP-MS combination was optimized by varying the concentration and flow-rate of two eluents (nitric acid and hydrochloric acid). The effects of varying the sample pH were assessed and the column capacity was determined by "breakthrough" tests. The elements copper, cadmium, mercury and lead were studied; the detection capability was dependent upon the sample volume loaded onto the column. The accuracy of the method was assessed by analysis of an "in house" reference standard.