Fingerprinting G-protein-coupled receptors

Recently we reported the design of a discriminating fingerprintfor rhodopsin-like G-protein-coupled receptors (GPCRs). Thefingerprint encodes the seven putative membrane-spanning motifsand was potently diagnostic of all GPCRs (52 in all) in version8.1 of the OWL composite sequence database, readily distinguishingthem from all other integral membrane proteins. With a 3-foldincrease in the size of OWL, the fingerprint has been updatedand now finds 332 receptors that match all the motifs. The situation,however, has grown in complexity: 61 sequences make imperfectmatches with the fingerprint, yielding a total of 393 ‘hits’.The bulk of the partial hits are olfactory receptors: theseappear to fall into discrete subfamilies in which one or moreof the transmembrane motifs are either poorly matched or arenot matched at all. These results are supported by preliminaryphylogenetic analyses, which show the olfactory and variousother partial matches clustering away from the main body oftrue hits. The approach has provided a powerful diagnostic toolfor identifying GPCRs, and results are consistent with previousobservations that the pheromone, cAMP and secretin-like receptorsbelong to separate families-these bear their own unique sequencefingerprints by which they may be distinguished from the rhodopsin-likesuperfamily     

Moisture absorption by cyanate ester modified epoxy resin matrices. Part I. Effect of spiking parameters

The moisture absorption of cyanate ester modified epoxy resin matrices has been studied under thermal spiking conditions. Enhanced moisture absorption has been observed at spike-temperatures above 120 °C. The results of the desorption studies on both control specimens and the spiked specimens showed that some of the water molecules remained entrained in the polymer. It is postulated that this water could be associated with that which is hydrogen bonded or from the hydrolysis of isolated residual cyanate ester groups because the concentration of entrained water remains constant at spike-temperatures below 180 °C. Above 180 °C a thermally activated process, leading to chain scission as indicated by a reduced recoverability of the glass transition temperature (T_g) on drying.On isothermal resorption, the moisture concentration was found to be similar to that achieved through thermal spiking, showing that the entrained water at the lower spike-temperatures can also be achieved under mild conditions. The T_g is reversibly recovered to within 5 °C, which indicates a degree of relaxation rather than degradation. The moisture diffusion coefficient estimated from the resorption curves is lower than those estimated from the absorption and desorption curves. The isothermal resorption diffusion coefficient also decreased with increasing spike temperature. It is proposed that thermal spiking induced a relaxation of the network but as the spike-temperature approaches the transition region of the wet polymer, further hydrolytically induced relaxation events become feasible.     

Farm-scale carbon and nitrogen fluxes in pastoral dairy production systems using different nitrogen fertilizer regimes

Nutrient Cycling in Agroecosystems - The nitrogen (N) fertilizer application rate (kg ha?1 year?1) in pastoral dairy systems affects the flow of N through the soil,...     

Diagnostics for the laser fusion program--Plasma physics on the scale of microns and picoseconds

Diagnostic techniques are reviewed in the context of insights they provide to physical processes dominating the implosion of laser fusion targets. Specific examples chosen from recent experiments demonstrate that adequate diagnostic techniques, resolved to microns and picoseconds, have been developed for the demanding requirements of laser driven "exploding pusher" targets. Future diagnostic needs are related to the special problems forseen with "ablatively driven" high density implosions.     

A Simple Bioconjugate Attachment Protocol for Use in Single Molecule Force Spectroscopy Experiments Based on Mixed Self-Assembled Monolayers

Single molecule force spectroscopy is a technique that can be used to probe the interaction force between individual biomolecular species. We focus our attention on the tip and sample coupling chemistry, which is crucial to these experiments. We utilised a novel approach of mixed self-assembled monolayers of alkanethiols in conjunction with a heterobifunctional crosslinker. The effectiveness of the protocol is demonstrated by probing the biotin-avidin interaction. We measured unbinding forces comparable to previously reported values measured at similar loading rates. Specificity tests also demonstrated a significant decrease in recognition after blocking with free avidin.     

Oral Sustained Delivery of Theophylline and Cimetidine from In Situ Gelling Pectin Formulations in Rabbits

ABSTRACT

The aim of this study was to evaluate the potential of an in situ gelling pectin formulation as a vehicle for the oral sustained delivery of theophylline and cimetidine. In vitro studies demonstrated diffusion-controlled release of theophylline from 1, 1.5, and 2% w/v pectin gels. Release of this drug from 1.5% w/v pectin gels formed in situ in rabbit stomach was sustained over a period of 12 hours giving a theophylline bioavailability some seven fold higher than when administered from a commercial syrup. In contrast, interactions between cimetidine and pectin led to weak gelation of the pectin sols that prevented any meaningful determination of in vitro release characteristics. Similarly, in vivo release profiles from pectin formulations containing cimetidine were similar to that from a solution of this drug in buffer, indicative of weak gelation. Examination of the content of the rabbit stomach 5 hours after administration of 1.5% w/v pectin sols containing drug confirmed gel formation, but gels containing cimetidine were noticeably softer than those containing theophylline.     

A SAXS study of the structure of gels formed by mixtures of polyoxyalkylene triblock copolymers

Small‐angle X‐ray scattering was used to characterise aqueous micellar gels of triblock copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂, E₇₆S₅E₇₆, E₆₂P₃₉E₆₂, and of two mixtures: E₁₃₇S₁₈E₁₃₇ and E₆₂P₃₉E₆₂ (Mix 1) and E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ (Mix 2), each 50/50 wt%. E = oxyethylene, CH₂CH₂O; S = oxyphenylethylene, OCH₂CH(C₆H₅); and P = oxypropylene, OCH₂CH(CH₃). Within the concentration and temperature ranges investigated (30–40 wt% copolymer, 20–80 °C), spherical micelles of copolymers E₁₃₇S₁₈E₁₃₇, E₈₂S₉E₈₂ and E₆₂P₃₉E₆₂ packed into body‐centred cubic (BCC) structures. Gels of E₇₆S₅E₇₆ were stable only at high concentrations and low temperatures, and a 70 wt% copolymer solution at T = 30 °C formed a hexagonal gel consistent with cylindrical micelles. It is likely that the mixed copolymers would form two distributions of micelles, and more complex structures were expected. However, gels of Mix 2 had well‐ordered BCC structures, while the less ordered gels of Mix 1 were also best characterised as BCC. Copyright © 2006 Society of Chemical Industry     

XAS and XPS characterization of mercury binding on brominated activated carbon

Brominated powdered activated carbon sorbents have been shown to be quite effective for mercury capture when injected into the flue gas duct at coal-fired power plants and are especially useful when burning Western low-chlorine subbituminous coals. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) have been used to determine information about the speciation and binding of mercury on two commercially available brominated activated carbons. The results are compared with similar analysis of a conventional (non-halogenated) and chlorinated activated carbon. Both the XAS and XPS results indicate that the mercury, though introduced as elemental vapor, is consistently bound on the carbon in the oxidized form. The conventional and chlorinated activated carbons appeared to contain mercury bound to chlorinated sites and possibly to sulfate species that have been incorporated onto the carbon from adsorbed SO2. The mercury-containing brominated sorbents appear to contain mercury bound primarily at bromination sites. The mechanism of capture for the sorbents likely consists of surface-enhanced oxidation of the elemental mercury vapor via interaction with surface-bound halide species with subsequent binding by surface halide or sulfate species.     

Thermally reversible xyloglucan gels as vehicles for rectal drug delivery

The aim of this study was to investigate the potential application of thermoreversible gels formed by a xyloglucan polysaccharide derived from tamarind seed for rectal drug delivery. Xyloglucan that had been partially degraded by beta-galactosidase to eliminate 44% of galactose residues formed gels at concentrations of between 1 to 2% w/w at gelation temperatures decreasing over the range 27 to 22 degreesC with increasing concentration. The in vitro release of indomethacin and diltiazem from the enzyme-degraded xyloglucan gels followed root-time kinetics over a period of 5 h at 37 degreesC; the diffusion coefficients increasing with temperature increase between 10 and 37 degreesC. The in vitro release of indomethacin from the gels was significantly more sustained than from commercial suppositories. Measurement of plasma levels of indomethacin after rectal administration to rabbits of the gels and commercial suppositories containing an identical drug concentration indicated a broader absorption peak following administration of the gels, and a longer residence time. There was no significant difference in bioavailability of indomethacin when administered by these two vehicles. Morphological studies of rectal mucosa following a single administration of the gels showed no evidence of tissue damage. The results of this study suggest the potential of the enzyme-degraded xyloglucan gels as vehicles for rectal delivery of drugs.