This Week in Science

Science  19 Jan 1996:
Vol. 271, Issue 5247, pp. 269
  1. Superconductor symmetry

    Experiments determining the pairing symmetry in copper oxide superconductors have strongly suggested d-wave pairing symmetry but have not ruled out s-wave states. Tsuei et al. (p. 329; see the cover and the news story by Clery, p. 288) have determined the pairing symmetry in a tricrystal film of thallium-barium copper oxide. They observed a half-integer quantum flux of spontaneous magnetization only over the intersection of the three grains, a result consistent with dx2-y2 symmetry.

  2. Sea change


    The Mediterranean Sea has vertical, thermohaline circulation like that in the major oceans. Deep water was formed since at least early this century in the Adriatic Sea. Recent surveys described by Roether et al. (p. 333) revealed that the pattern changed after 1987. Deep water is now forming in the Aegean Sea, apparently because of an increase in the salinity of surface waters there.

  3. Leading lights

    Materials that exhibit the electro-optic effect, a nonlinear optical property, change their refractive index in response to an applied electric field and could be used to process signals in fiber-optic networks. Ahlheim et al. (p. 335) synthesized polymers containing conjugated donor-acceptor chromophores with strongly electron-withdrawing acceptors. After a process that aligns the chromophores, one of these materials had an electro-optic coefficient twice that of lithium niobate at 1.3 micrometers, a wavelength used in telecommunications.

  4. Galactic shapes

    Astronomers can only make two-dimensional images of distant objects, a process that loses most shape information. Elliptical galaxies present a particular challenge as they could be oblate, prolate, or triaxial. Merritt (p. 337) modeled how stars orbit within elliptical galaxies and found that chaotic trajectories prevent evolution toward triaxial equilibrium. Most such galaxies are likely axisymmetric, that is, prolate or oblate.

  5. CFC destruction

    As chlorofluorocarbons (CFCs) are recovered and replaced with more benign substitutes, the problem remains of disposing these normally unreactive gases. Burdeniuc and Crabtree (p. 340) show that passing CFCs over a hot bed of sodium oxalate (Na2C2O4) converts them to salts (NaCl and NaF), carbon, and CO2. A similar reaction converts saturated fluorocarbons into aromatic species.

  6. Adjuvant internal

    The products of acquired immune response, such as antibodies, often exert their effect by enhancing inate mechanisms of immunity, such as phagocytosis. Dempsey et al. (p. 348) report that the complement component C3d acts like an adjuvant—its attachment to a protein antigen enhances the antibody response by a factor of up to 10,000, a finding that may prove useful in peptide and protein vaccine development.

  7. Suppressing like Mad

    About 90% of human pancreatic cancers display allelic loss at chromosome 18q, a finding that strongly suggests the presence of a tumor suppressor gene. Hahn et al. (p. 350; see the news story by O'Brien, p. 294) identified a strong candidate suppressor gene at 18q21.1 that is deleted or mutated in a significant fraction of pancreatic cancers. The DPC4 gene (for deleted in pancreatic carcinoma), is similar in sequence to the Drosophila Mad gene, mutations in which produce abnormalities in midgut morphogenesis, imaginal disc development, and dorsal-ventral patterning. The Mad gene has been implicated in a transforming growth factor-β-like signaling pathway.

  8. Putting down patterns

    Bone morphogenetic proteins (BMPs) induce the formation of cartilage and bone in mammals. BMP-1 has metalloproteinase activity and is similar to proteins that control morphogenetic patterning in Drosophila. Kessler et al. (p. 360) report that human BMP-1 is identical to procollagen C-proteinase (PCP), the enzyme that cleaves procollagen into monomers that form collagen fibrils. In addition to its proposed role in activating other BMPs, which are members of the transforming growth factor-β family, BMP-1 may influence pattern formation by controlling deposition of extracellular matrix.

  9. Endocytosis adaptor

    After binding their ligands, certain receptors are internalized. For the beta2-adrenergic receptor (beta2AR), a member of a large family of receptors involved in signal transduction, ligand binding inactivates the receptor for further signal transduction and internalization must occur to reactivate the receptor. Ferguson et al. (p. 363) examined the role of the protein β-arrestin, which interacts with beta2AR, in this process. The protein can stimulate the internalization and reactivation of mutant receptors that are deficient in these processes. Thus a cytosolic protein that is not part of the constitutive endocytic machinery can specifically modulate internalization.

  10. Zinc and epilepsy

    In the brain, synaptic excitation and inhibition must be carefully balanced. Reduced synaptic inhibition results in hyperexcitability and epilepsy. Paradoxically, in an animal model of temporal lobe epilepsy, inhibition mediated by γ-aminobutyric acid (GABA) receptors appears to be increased rather than decreased. Buhl et al. (p. 369) found that these GABA receptors are more sensitive to zinc compared to those from normal animals. Zinc can break down the otherwise increased inhibition of neurotransmission mediated by the GABA receptors in temporal lobe epilepsy. Zinc can also be released in the mossy fibers found in the brains of epilepsy patients.

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