Bioaccumulation and excretion of arsenic compounds by a marine unicellular alga,polyphysa peniculus

Polyphysa peniculus was grown in artificial seawater in the presence of arsenate, arsenite, monomethylarsonate and dimethylarsinic acid. The separation and identification of some of the arsenic species produced in the cells as well as in the growth medium were achieved by using hydride generation–gas chromatography–atomic absorption spectrometry methodology. Arsenite and dimethylarsinate were detected following incubation with arsenate. When the alga was treated with arsenite, dimethylarsinate was the major metabolite in the cells and in the growth medium; trace amounts of monomethylarsonate were also detected in the cells. With monomethylarsonate as a substrate, the metabolite is dimethylarsinate. Polyphysa peniculus did not metabolize dimethylarsinic acid when it was used as a substrate. Significant amounts of more complex arsenic species, such as arsenosungars, were not observed in the cells or medium on the evidence of flow injection–microwave digestion–hydride generation–atomic absorption spectrometry methodology. Transfer of the exposed cells to fresh medium caused release of most cell–associated arsenicals to the surrounding environment.     

Orientation and relaxation of polymer–clay solutions studied by rheology and small-angle neutron scattering

The influence of shear on viscoelastic solutions of poly(ethylene oxide) (PEO) and clay [montmorillonite, i.e., Cloisite NA+ (CNA)] was investigated with rheology and small-angle neutron scattering (SANS). The steady-state viscosity and SANS were used to measure the shear-induced orientation and relaxation of the polymer and clay platelets. Anisotropic scattering patterns developed at much lower shear rates than in pure clay solutions. The scattering anisotropy saturated at low shear rates, and the CNA clay platelets aligned with the flow, with the surface normal parallel to the gradient direction. The cessation of shear led to partial and slow randomization of the CNA platelets, whereas extremely fast relaxation was observed for laponite (LRD) platelets. These PEO–CNA networklike solutions were compared with previously reported PEO–LRD networks, and the differences and similarities, with respect to the shear orientation, relaxation, and polymer–clay interactions, were examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3102–3112, 2004     

Characterization of dynamic and steady-state protein phosphorylation using a fluorescent phosphoprotein gel stain and mass spectrometry

Protein phosphorylation plays a vital role in the regulation of most aspects of cellular activity, being key to propagating messages within signal transduction pathways and to modulating protein function. Pro-Q Diamond phosphoprotein gel stain is suitable for the fluorescence detection of phosphoserine-, phosphothreonine-, and phosphotyrosine-containing proteins directly in sodium dodecyl sulfate (SDS)-polyacrylamide gels. The technology is especially appropriate for profiling steady-state and dynamic phosphorylation on a proteome-wide scale, as demonstrated through detection of the native phosphorylation of cardiac mitochondrial phosphoproteins and changes in this profile arising from the activity of a protein kinase. For example, Pro-Q Diamond phosphoprotein gel stain was employed to demonstrate that among the 46 subunits of the mitochondrial respiratory chain complex, NADH:ubiquinone oxidoreductase (complex I), a 42 kDa subunit is phosphorylated in the steady-state. However, exposure of mitochondria to cAMP-dependent protein kinase increases phosphorylation of this 42 kDa subunit and results in de novo phosphorylation of an 18 kDa subunit as well. Since Pro-Q Diamond dye binds to phosphorylated residues noncovalently, the staining technology is fully compatible with modern microchemical analysis procedures, such as peptide mass profiling by matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and post-source decay analysis of peptide phosphorylation.     

Cyclophosphamides from aminosugars and aminonucleosides

Condensation of bis-(2-chloroethyl)phosphoramidic dichloride with 3′-amino-3′-deoxy-N,N-dimethyladenosine afforded the 2′,3′-cyclicphosphorodiamidate (III). By an improved synthesis, methyl 3-amino-3-deoxy-β-D-ribofuranoside was obtained as a model compound for conversion to the analogous 2,3-cyclicphosphorodiamidate (XII). Existence of the latter as two diastereomers due to phosphorus asymmetry was shown by nmr analysis, using comparison with the 5-(O-p-nitrobenzoate) (XIII) as a basis for assignments.     

Wannier-Stark effect on surface states

A recursive Green-function (RGF) technique is used to study the surface states of an electrified solid. The concatenating nature of the method leads to a continued-fraction form of the RGF, which can be expressed as a ratio of Bessel functions. The surface density of states (SDOS), derived from the RGF, reveals a quasi-Stark-ladder distribution of the energy levels at the surface atom. The dependence of the SDOS on the applied field and surface perturbation parameters is discussed.     

Detection of phosphoproteins on electroblot membranes using a small-molecule organic fluorophore

A new formulation of the small-molecule organic fluorophore, Pro-Q Diamond dye, has been developed that permits rapid and simple detection of phosphoproteins directly on polyvinylidene difluoride (PVDF) or nitrocellulose membranes (electroblots). Protein samples are first separated by electrophoresis and then electroblotted to membranes, stained and destained, in an analogous manner as typically performed with Amido Black or Ponceau S dye staining of total protein profiles. After staining, blots are imaged using any of a variety of laser-based gel scanners, xenon-arc lamp-based gel scanners or charge-coupled device (CCD) camera-based imaging devices equipped with UV trans- or epi-illumination. The uncomplicated and reliable staining protocol delivers results in as little as 1 h and the limit of detection for the stain is typically 2-4 ng of phosphoprotein with a linear dynamic range of approximately 15-fold. Compared with traditional radiolabeling and antibody-based approaches, the new method offers significant advantages, including avoidance of radioactivity, no need for expensive antibodies, no requirement for blocking unoccupied sites on the membrane with protein or detergent solutions, no sequence context-specific binding to phosphorylated amino acid residues and the ability to analyze the native, steady-state phosphorylation of proteins obtained directly from tissue specimens or body fluids. Pro-Q Diamond dye binds directly and exclusively to the phosphate moiety, allowing it to detect the broadest spectrum of phosphorylated proteins possible. The stain binds noncovalently to phosphoproteins and is thus fully compatible with matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) or Edman sequencing. The blot stain is also compatible with standard colorimetric, fluorogenic, and chemiluminescent detection techniques employed in immunoblotting.     

Enantioselective synthesis of alpha-methyl-D-cysteine and lanthionine building blocks via alpha-methyl-D-serine-beta-lactone

[reaction: see text] We report here the enantioselective synthesis of Boc-alpha-methyl-d-cysteine(PMB)-OH and lanthionine building blocks through the regioselective ring opening of key intermediate Boc-alpha-methyl-d-serine-beta-lactone.