Visual function: How spiders find the right rock to crawl under

Animals that go on hunting expeditions face the problem of finding the way home at the end of the day. A group of hunting spiders has now been added to the list of animals that use the celestial pattern of polarized light as a compass for navigation. (C) 1999 Elsevier Science Ltd. All rights reserved.

What the evolution of the amyloid protein precursor supergene family tells us about its function

The Alzheimer's disease amyloid protein precursor (APP) gene is part of a multi-gene super-family from which sixteen homologous amyloid precursor-like proteins (APLP) and APP species homologues have been isolated and characterised. Comparison of exon structure (including the uncharacterised APL-1 gene), construction of phylogenetic trees, and analysis of the protein sequence alignment of known homologues of the APP super-family were performed to reconstruct the evolution of the family and to assess the functional significance of conserved protein sequences between homologues. This analysis supports an adhesion function for all members of the APP super family, with specificity determined by those sequences which are not conserved between APLP lineages, and provides evidence for an increasingly complex APP superfamily during evolution. The analysis also suggests that Drosophila APPL and Caenorhabdotids elegans APL-1 may be a fourth APLP lineage indicating that these proteins, while not functional homologues of human APP, are similarly likely to regulate cell adhesion. Furthermore, the beta A4 sequence is highly conserved only in APP orthologues, strongly suggesting this sequence is of significant functional importance in this lineage. (C) 2000 Elsevier Science Ltd. All rights reserved.

Single-spin measurement using single-electron transistors to probe two-electron systems

We present a method for measuring single spins embedded in a solid by probing two-electron systems with a single-electron transistor (SET). Restrictions imposed by the Pauli principle on allowed two-electron states mean that the spin state of such systems has a profound impact on the orbital states (positions) of the electrons, a parameter which SET's are extremely well suited to measure. We focus on a particular system capable of being fabricated with current technology: a Te double donor in Si adjacent to a Si/SiO2, interface and lying directly beneath the SET island electrode, and we outline a measurement strategy capable of resolving single-electron and nuclear spins in this system. We discuss the limitations of the measurement imposed by spin scattering arising from fluctuations emanating from the SET and from lattice phonons. We conclude that measurement of single spins, a necessary requirement for several proposed quantum computer architectures, is feasible in Si using this strategy.

Sulfite : Cytochrome c oxidoreductase from Thiobacillus novellus - Purification, characterization, and molecular biology of a heterodimeric member of the sulfite oxidase family

Direct oxidation of sulfite to sulfate occurs in various photo- and chemotrophic sulfur oxidizing microorganisms as the final step in the oxidation of reduced sulfur compounds and is catalyzed by sulfite:cytochrome c oxidoreductase (EC 1.8.2.1), Here we show that the enzyme from Thiobacillus novellus is a periplasmically located alpha beta heterodimer, consisting of a 40.6-kDa subunit containing a molybdenum cofactor and an 8.8-kDa monoheme cytochrome c(552) smbunit (midpoint redox potential, Em(8.0) = +280 mV), The organic component of the molybdenum cofactor was identified as molybdopterin contained in a 1:1 ratio to the Mo content of the enzyme. Electron paramagnetic resonance spectroscopy revealed the presence of a sulfite-inducible Mo(V) signal characteristic of sulfite:acceptor oxidoreductases. However, pH-dependent changes in the electron paramagnetic resonance signal were not detected. Kinetic studies showed that the enzyme exhibits a ping-pong mechanism involving two reactive sites. K-m values for sulfite and cytochrome c(550) were determined to be 27 and 4 mu M, respectively; the enzyme was found to be reversibly inhibited by sulfate and various buffer ions. The sorAB genes, which encode the enzyme, appear to form an operon, which is preceded by a putative extracytoplasmic function-type promoter and contains a hairpin loop termination structure downstream of sorB. While SorA exhibits significant similarities to known sequences of eukaryotic and bacterial sulfite:acceptor oxidoreductases, SorB does not appear to be closely related to any known c-type cytochromes.

Adhesion of microbes using 3-aminopropyl triethoxy silane and specimen stabilisation techniques for analytical transmission electron microscopy

A variety of adhesive support-films were tested for their ability to adhere various biological specimens for transmission electron microscopy. Support films primed with 3-amino-propyl triethoxy silane (APTES), poly-L-lysine, carbon and ultraviolet-B (UV-B)-irradiated carbon were tested for their ability to adhere a variety of biological specimens including axenic cultures of Bacillus subtilis and Escherichia coli and wild-type magnetotactic bacteria. The effects of UV-B irradiation on the support film in the presence of air and electrostatic charge on primer deposition were tested and the stability of adhered specimens on various surfaces was also compared. APTES-primed UV-B-irradiated Pioloform(TM) was consistently the best adhesive, especially for large cells, and when adhered specimens were UV-B irradiated they became remarkably stable under an electron beam. This assisted the acquisition of in situ phase-contrast lattice images from a variety of biominerals in magnetotactic bacteria, in particular metastable greigite magnetosomes. Washing tests indicated that specimens adhering to APTES-primed UV-B-irradiated Pioloform(TM) were covalently coupled. The electron beam stability was hypothesised to be the result of mechanical strengthening of the specimen and support film and the reduced electrical resistance in the specimen and support film due to their polymerization and covalent coupling.

Field-swept pulsed electron paramagnetic resonance of Cr3+-doped ZBLAN fluoride glass

Field-swept pulsed electron paramagnetic resonance (EPR) spectra of a ZBLAN fluoride glass doped with a low concentration of Cr3+ are obtained using echo-detected EPR and hole-burning free induction decay detection. We review the utility of the pulsed EPR technique in generating field-swept EPR spectra, as well as some of the distorting effects that are peculiar to the pulsed detection method. The application of this technique to Cr3+-doped ZBLAN reveals that much of the broad resonance extending from g(eff) = 5.1 to g(eff) = 1.97, characteristic of X-band continuous wave EPR of Cr3+ in glasses, is absent. We attribute this largely to the variation in nutation frequencies across the spectrum that result from sites possessing large fine structure interactions. The description of the spin dynamics of such sites is complicated and we discuss some possible approaches to the simulation of the pulsed EPR spectra.

Autonomic activity during human sleep as a function of time and sleep stage

While there is a developing understanding of the influence of sleep on cardiovascular autonomic activity in humans, there remain unresolved issues. In particular, the effect of time within the sleep period, independent of sleep stage, has not been investigated. Further, the influence of sleep on central sympathetic nervous system (SNS) activity is uncertain because results using the major method applicable to humans, the low frequency (LF) component of heart rate Variability (HRV), have been contradictory, and because the method itself is open to criticism. Sleep and cardiac activity were measured in 14 young healthy subjects on three nights. Data was analysed in 2-min epochs. All epochs meeting specified criteria were identified, beginning 2 h before, until 7 h after, sleep onset. Epoch values were allocated to 30-min bins and during sleep were also classified into stage 2, slow wave sleep (SWS) and rapid eye movement (REM) sleep. The measures of cardiac activity were heart irate (HR), blood pressure (BP), high frequency (HF) and LF components of HRV and pre-ejection period (PEP). During non-rapid eye movement (NREM) sleep autonomic balance shifted from sympathetic to parasympathetic dominance, although this appeared to be more because of a shift in parasympathetic nervous system (PNS) activity. Autonomic balance during REM was in general similar to wakefulness. For BP and the HF and LF components the change occurred abruptly at sleep onset and was then constant over time within each stage of sleep, indicating that any change in autonomic balance over the sleep period is a consequence of the changing distribution of sleep stages. Two variables, HR and PEP, did show time effects reflecting a circadian influence over HR and perhaps time asleep affecting PEP. While both the LF component and PEP showed changes consistent with reduced sympathetic tone during sleep, their pattern of change over time differed.

CD40 ligation conditions dendritic cell antigen-presenting function through sustained activation of NF-kappa B

An understanding of the biochemical control of dendritic cell (DC) differentiation/activation is essential for improving T cell immunity by various immunotherapeutic approaches, including DC immunization. Ligation of CD40 enhances DC function, including conditioning for CTL priming. NF-kappaB, and particularly RelB, is an essential control pathway for myeloid DC differentiation. Furthermore, RelB regulates B cell Ag-presenting function. We hypothesized that CD40 ligand (CD40L) and TNF-alpha, which differ in their capacity to condition DC, would also differ in their capacity to activate NF-kappaB. DC differentiated for 2 days from monocytes in the presence of GM-CSF and IL-4 were used as a model, as NF-kappaB activity was constitutively low. The capacity of DC to activate T cells following CD40L treatment was enhanced compared with TNF-alpha treatment, and this was NF-kappaB dependent. Whereas RelB/p50 translocation induced by TNF-alpha was attenuated after 6 h, RelB/p50 nuclear translocation induced by CD40L was sustained for at least 24 h. The mechanism of this difference related to enhanced degradation of IkappaBalpha following CD40L stimulation. However, NF-kappaB activation induced by TNF-alpha could be sustained by blocking autocrine IL-10. These data indicate that NF-kappaB activation is essential for T cell activation by DC, and that this function is enhanced if DC NF-kappaB activation is prolonged. Because IL-10 moderates DC NF-kappaB activation by TNF-alpha, sustained NF-kappaB activation can be achieved by blocking IL-10 in the presence of stimuli that induce TNF-alpha.

Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function

In this study the variations in surface reflectance properties and pigment concentrations of Antarctic moss over species, sites, microtopography and with water content were investigated. It was found that species had significantly different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm), but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in the visible region and in the characteristics of the red edge over different sites. Reflectance parameters, such as the photochemical reflectance index (PRI) and cold hard band were useful discriminators of site, microtopographic position and water content. The PRI was correlated both with the concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, F-v/F-m, measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and position of the red-edge as well as the PRI, and may be responsible for observed differences in reflectance properties for different species and sites. All moss showed sustained high levels of photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing continual high levels of photochemical stress.

On the theory of mixing-frequency electron spin-echo envelope modulation spectroscopy

It has recently been stated that the parametrization of the time variables in the one-dimensional (I-D) mixing-frequency electron spin-echo envelope modulation (MIF-ESEEM) experiment is incorrect and hence the wrong frequencies for correlated nuclear transitions are predicted. This paper is a direct response to such a claim, its purpose being to show that the parametrization in land 2-D MIF-ESEEM experiments possesses the same form as that used in other 4-pulse incrementation schemes and predicts the same correlation frequencies. We show that the parametrization represents a shearing transformation of the 2-D time-domain and relate the resulting frequency domain spectrum to the HYSCORE spectrum in terms of a skew-projection. It is emphasized that the parametrization of the time-domain variables may be chosen arbitrarily and affects neither the computation of the correct nuclear frequencies nor the resulting resolution. The usefulness or otherwise of the MIF parameters \gamma\ > 1 is addressed, together with the validity of the original claims of the authors with respect to resolution enhancement in cases of purely homogeneous and inhomogeneous broadening. Numerical simulations are provided to illustrate the main points.