This Week in Science

Science  07 Mar 1997:
Vol. 275, Issue 5305, pp. 1393
  1. Fixating on nitrogen

    Two reports shed new light on nitrogen (N2) fixation by transition metal complexes (see the Perspective by Leigh, p. 1442). In the presence of hydrogen (H2), the efficiency of nitrogenase enzymes is reduced, apparently by displacement of the N2 without chemical transformation. Fryzuk et al. (p. 1445) studied a zirconium complex containing N2 and found that a bridging complex involving H2 can be formed, showing that transformation of N2 can result from the addition of H2. Shan et al. (p. 1460) show that N2 can be housed within six gold atoms inside a “cage” formed by two sets of three gold atoms, a binding geometry that has little precedent in N2 chemistry. Although the chemistry of this system is quite different (nitrogenases do not contain gold), this result may help resolve how the N2 molecule is accommodated in the nitrogenase cluster.

  2. Controls wetness

    Polymer scientists often combine different polymers to tailor surface properties, such as adhesion and wetting, but in some cases segregation of one component that can lead to dewetting and delamination. Mansky et al. (p. 1458) grafted copolymers onto a silica substrate to form 5-nanometer-thick “brushes.” These consisted of polystyrene (PS) and poly(methylmethacrylate) (PMMA) assembled randomly onto the growing chain by living polymerization methods. An optimal PS-PMMA ratio was found that had equal affinities for both polymers.

  3. First in flight?

    The oldest known flying reptile is Coelurosauravus jaekeli, which lived during the Permian more than 250 million years ago. It evidently flew by gliding and had an unusual wing structure that was thought to be formed by elongated ribs. Frey et al. (p. 1450; see the news story by Wuethrich, p. 1419) describe a complete skeleton of this reptile found in Germany that shows that the wings were supported by long bony rods of dermal origin and a long tail.

  4. Ocean mixing

    An important question in understanding the carbon cycle and ocean nutrient supply, and in climate modeling, is the extent that deep waters upwell and reach the surface. One tracer for this process is carbon isotopes because old deep waters are depleted in carbon-14, which forms in the upper atmosphere. Examination of carbon ratios in coral provides a record of exchange over time. Druffel (p. 1454) shows that corals from Bermuda record decadal shifts in carbon-14-carbon-12 ratios that evidently reflect brief episodes of mixing between surface and deeper waters.

  5. Dwelling on the negative in optical computing

    Optical computing and image processing can both benefit from methods that directly record decreases in light intensity, but most measurements record only positive values. Lewis et al. (p. 1462) prepared a high-quality optical film containing the protein bacteriorhodopsin (bR), which can interconvert between two photoproducts with either blue or yellow light. Achromatic lenses are used to focus the blue and yellow light differently so that the amounts of photoproducts formed can represent mathematically the difference of two Gaussian functions or can be used to detect the edge of an object. The photoproducts have different charge states, so it should be possible to record the images electrically.

  6. Complex metabolism

    Insulin modulates the activity of many metabolic enzymes by promoting their dephosphorylation, a process mediated by protein phosphatase 1 (PP1). Printen et al. (p. 1475) identified a protein in insulin-sensitive tissues that binds to the catalytic subunit of PP1 and targets it to glycogen. This new protein, called PTG, also forms complexes with phosphorylase kinase, phosphorylase a, and glycogen synthase—the key enzymes involved in hormonal regulation of glycogen metabolism. The authors suggest that PTG may act as a molecular scaffold, assembling these enzymes onto the glycogen particle for localized reception of hormonal signals.

  7. Algae origin

    Apicomplexian parasites (such as the malaria parasite), in addition to nuclear and mitochrondrial genes, contain a 35-kilobase circular DNA molecule. Köhler et al. (p. 1485; see the news story by Vogel, p. 1422) used in situ hybridization to localize this DNA molecule in another organism, Toxoplasma gondii, to a discrete organelle surrounded by four membranes. These results, in combination with a phylogenetic analysis, indicate that this structure is a plastid related to green algal photosynthetic plastids. This organelle was likely captured directly from a green alga. Although its function is still unknown, its unusual nature may make it a useful therapeutic target.

  8. HIV-1 and immune hyperactivity

    A consequence of infection with human immunodeficiency virus-type 1 (HIV-1) is chronic hyperactivation of the immune system, a state that maintains infection because HIV-1 cannot infect resting T cells. Ott et al. (p. 1481) show that infection of peripheral human blood leukocytes in vitro with HIV-1-stimulated production of interleukin-2 (IL-2) when the cells were activated by T cells through the CD3 and CD28 receptors. Secreted IL-2 could cause noninfected cells to be more responsive toward activation in confined environments such as the lymph nodes. The same IL-2 response occurred in cells costimulated by CD3 and CD28 that expressed the HIV-1 transcriptional activator Tat; the second exon of Tat interacts with the CD28 pathway to stimulate IL-2 transcription.

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