Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

A simplified HPLC method for simultaneously quantifying ribonucleotides and deoxyribonucleotides in cell extracts or frozen tissues

Agents and conditions that induce alterations in deoxyribonucleotide pools can have important regulatory effects on the rate of DNA synthesis as well as cell cycle progression. A simplified procedure for the separation of both ribonucleoside triphos-phates (NTP) and deoxyribonucleoside triphosphates (dNTP) is presented which utilizes reversed phase high-performance liquid chromatography coupled with diode array detection. The simultaneous resolution of NTP and dNTP peaks within the same cell extract effectively eliminates the need for post-extraction steps such as periodate oxidation and/or boronate affinity chromatography previously used to degrade or isolate co-eluting NTP from dNTP. The resolution of two nucleotides, dGTP and ADP, was found empirically to vary with the efficiency of the C18 column. High efficiency columns (>90 000 plates/m) provided good separation; however, less efficient columns resulted in co-elution of dGTP and ADP. These co-eluting nucleotides can be accurately quantified, if necessary, using diode array technology and a mathematical expression which incorporates molar peak coefficients and peak areas obtained by monitoring at dual wavelengths. Tissue samples or single cell suspensions were extracted with trichloroacetic acid and the neutralized extract was injected directly into the column without prior lyophilization. The per cent recovery of standards was .99% and replicate extractions within or between samples were highly reproducible (sd<5%). The single step method described minimizes potential losses associated with post-extraction manipulation and provides the capability to examine alterations in nucleotide precursor–product metabolism under various physiological and pharmacological conditions.     

Identification of the Serratia endonuclease dimer: structural basis and implications for catalysis.

The Serratia endonuclease is an extracellularly secreted enzyme capable of cleaving both single- and double-stranded forms of DNA and RNA. It is the first member of a large class of related and usually dimeric endonucleases for which a structure is known. Using X-ray crystallography, the structure of monomer of this enzyme was reported by us previously (Miller MD et al., 1994, Nature Struct Biol 1:461-468). We now confirm the dimeric nature of this enzyme through light-scattering experiments and identify the physiologic dimer interface through crystal packing analysis. This dimerization occurs through an isologous twofold interaction localized to the carboxy-terminal subdomain of the enzyme. The dimer is a prolate ellipsoid with dimensions 30 A x 35 A x 90 A. The dimer interface is flat and contains four salt links, several hydrogen bonds, and nonpolar interactions. Buried water is prominent in this interface and it includes an unusual "cubic" water cluster. The position of the two active sites in the dimer suggests that they can act independently in their cleavage of DNA, but have a geometrical advantage in attacking substrate relative to the monomer.     

The effect of an interleukin receptor antagonist (IL-1ra) on colonocyte eicosanoid release

We investigated whether an interleukin 1 receptor antagonist (IL-1ra) altered cellular release of prostanoids and leukotrienes in a transformed colonic cell line (CACO-2) in the presence of proinflammatory stimuli. Cellular inflammation was induced by treatment with lipopolysaccharide (LPS) or the cytokine, interleukin 1 beta (IL-1(beta)). In a separate set of experiments, cells were pretreated with IL-1ra prior to exposure to LPS or IL-1(beta). Prostaglandin E(2) and leukotriene B(4) (LTB(4)) levels were quantified by ELISA assays. Both LPS and IL-1(beta) exposure were noted to stimulate cellular PGE(2) release, a response which was significantly inhibited by IL-1ra treatment. Either stimulant when administered alone failed to stimulate release of LTB(4). When administered after IL-1ra pretreatment however, both stimuli caused a significant increase in LTB(4) release. These results suggest that a cytokine receptor antagonist can selectively influence eicosanoid production in this cell line. Furthermore, this study suggests that a IL-1ra may have a future clinical role in the treatment of inflammatory disorders of the colon which are intimately linked to enhanced eicosanoid synthesis.     

Effect of subzero incubation on fluoride binding by laccase

We have refined a useful incubation method for preparing adducts of tree laccase with inhibitor anions; however, the technique should have wider application. The procedure involves incubating a previously frozen aqueous solution at subzero temperature. Factors influencing the amount of adduct that forms include the nature of the buffer, pH changes that occur at subzero temperatures and the presence of glycerol. In the absence of a glassing agent like glycerol, the phase separation and solute pooling that occur with ice formation help drive adduct formation. The results reveal several important factors to consider in designing or interpreting low-temperature spectroscopic investigations.     

Morphotypes of friable embryogenic maize callus

Friable, embryogenic callus cultures of maize are normally maintained as a heterogeneous mixture of various morphotypes in different stages of development (Fransz and Schel 1991). With stringent selection during subculture, three Type II callus morphotypes have been enriched and maintained. Cultured tissue segments from the three morphotypes referred to as pre-embryogenic, early embryogenic, and late embryogenic were analyzed using light and scanning electron microscopy. The results suggest a developmental relationship between the three morphotypes. Regeneration studies substantiated that all morphotypes were capable of regenerating through somatic embryogenesis.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine - MS Murashige and Skoog(1962) Medium - SEM Scanning Electron Microscopy - FAA Formalin-acetic acid-alcohol