JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. We use a phylogeny of the North American Enallagma damselflies, derived from molecular and morphological data, to examine how the patterns of local and regional assemblage structure developed in this taxon across eastern North America. The two primary clades in the genus have nearly identical numbers of extant species, but the centers of diversity and the diversification rates for the two clades are quite different. One clade has its center of diversity in New England and radiated very recently from three species to give the current 18. Although most of this radiation involved the creation of new species in the ancestral fish-lake habitat, at least two independent lineages invaded and adapted to a new habitat: ponds and lakes lacking fish but supporting large numbers of large predatory dragonflies. The other clade, with greatest diversity in the southeastern United States, contains species that inhabit only water bodies that support fish populations. This "southeastern" clade diversified at a much slower and more steady pace within the fish-lake habitat than the "New England" clade, but four speciation events in this clade appear to have occurred at the same time as the northern radiation. Combined with our current understanding of local community structure in fish and fishless lakes, these results indicate that most of the species in this regional assemblage were created by speciation mechanisms other than filling empty niches, which have resulted in many locally coexisting species that are very similar in their ecological characteristics. Damselflies in eastern North American ponds and lakes appear to exemplify features of both a regulated component of the littoral food web (i.e., a functional group) and an assemblage whose local community composition is influenced by nonadaptive macroevolutionary processes that have operated on a much larger regional scale. . Therefore, understanding community structure across these disparate scales (i.e., local, regional, biogeographic) requires that we study how processes operating at these various scales interact. Conceptually, ecologists have generally approached these issues by assuming a paradigm in which a defined regional pool of species exists, and each member of the pool can potentially colonize every local site within a biogeographic region (e.g., Diamond 1975, Post and Lockwood et al. 1997). The abiotic environment and species interactions determine which species can and cannot exist at each local site; some set of species from the regional pool can coexist at a given site, and the rest are driven locally extinct. ...

Solid-state NMR spectra with single-site resolution of CXCR1, a G protein-coupled receptor (GPCR), were obtained in magnetically-aligned phospholipid bicelles. These results demonstrate that GPCRs in phospholipid bilayers are suitable samples for structure determination by solid-state NMR. The spectra also enable studies of drug-receptor interactions.G protein-coupled receptors (GPCRs) are prized targets for structure determination; however, with seven transmembrane helices and more than 300 residues, they are also among the most challenging. Strategically located in the membrane, these proteins regulate the physiological functions of cells in response to external chemical signals. The information is transmitted through the membrane by a change in conformation, and the resulting activation of a cognate G protein triggers myriad signaling pathways in the cytoplasm. About 1000 GPCRs have been identified in the human genome. Although most are for sensory functions, several hundred are potential drug receptors.The structure of only one GPCR has been determined, and that is of rhodopsin 1 , which responds to photons and not chemical ligands. Although efforts are being made to model GPCRs on the structure of rhodopsin and with other computational methods 2 , it is essential to determine their individual three-dimensional structures in order to understand their mechanisms of action and for structure-based drug design. A number of NMR studies of rhodopsin have been reported that illustrate the complexities encountered in applying both solution NMR to micelle 3 and magic angle spinning solid-state NMR to bilayer 3a, 4 samples of polytopic membrane proteins.

What people think about food nanotechnology (nanofood) is under‐explored in the United States, especially outside of quantitative surveys. As such, we set out to examine public attitudes toward food nanotechnology in conversational, focus group settings in order to identify policy options for nanofood governance, and in particular, options for labeling. Through analysis of focus groups in six U.S. locations, we found that the vast majority of the participants wanted nanotechnology labels for all types of food products, and most were willing to pay a premium for labeling. Participants cited abilities to choose and avoid potential risk as the main purposes of nanofood labels. However, they recognized that labels alone do not provide much meaning and that information concerning food nanotechnology products needs to be sought and supplied beyond the label to enable informed choices. Additionally, willingness‐to‐use and risk–benefit perceptions varied according to the position and intended functions of the nanomaterials in food products.

The case depth of induction-hardened steel rods has been determined using multi-frequency alternating current potential-drop measurements. Experimental results are analyzed using a model which approximates the variation in the material properties of a hardened rod by assuming that a homogeneous core is surrounded by a homogeneous case-hardened layer of uniform thickness. Experimental measurements on an untreated rod are used to estimate the core conductivity and permeability of similar hardened rods. The implicit assumption is that the material parameters in the core region are unchanged in the hardening process. The case depth is found by parameter fitting to minimize a penalty function representing the overall difference between multi-frequency potential-drop measurements and theoretical predictions. Case-depth values found nondestructively show reasonable agreement with those found using Rockwell hardness measurements on sectioned rods.

Most secreted eukaryotic proteins are modified by glycosylation, and it has been difficult to solve their structures by crystallographic or NMR techniques because of problems posed by the presence of the carbohydrate. The structure of a chemically deglycosylated form of the human pregnancy hormone, human chorionic gonadotropin (hCG), has been solved by crystallographic methods. Since chemical deglycosylation may have induced changes in the structure, and since it is known that deglycosylated hCG is biologically inactive, the crystallographic structure confirmation by NMR techniques. Also, it has not been possible to determine the structures of the isolated subunits, nor the nature of interactions between the carbohydrate side chains and the protein backbone by crystallographic methods. Structural information via NMR techniques can be obtained from proteins in solution if they can be uniformly labeled with 13C and 15N isotopes. We report the first such uniform labeling of a glycoprotein using a universal 13C- and 15N-labeling medium to express 13C, 15N-labeled hCG, suitable for solving the structure in solution of the native, biologically active form of hCG as well as that of its free subunits. The 13C, 15N-labeled recombinant hCG and its separated subunits are shown to be nearly identical to urinary hCG reference preparations on the basis of protein chemical studies, immunochemistry, biological activity, and the capability of isolated hormone subunits to recombine to form biologically active hormone. Mass spectrometric analysis and preliminary NMR studies indicate that the isotopic labeling is uniform and greater than 90% after only two growth passages in the labeling media. One unexpected finding during subunit purification was that lyophilization of glycoproteins from trifluoroacetic acid HPLC buffers may result in the loss of a significant portion of sialic acid.