Calcium regulation of molluscan myosin ATPase in the absence of actin

In the myosin-linked regulatory mechanism typified by the molluscan scallop adductor muscle, contraction is controlled by Ca2+ binding to sites on the thick filament protein, myosin. The regulatory light chains of myosin heads are involved directly in this mechanism and early studies suggested that, in the absence of Ca2+, these subunits prevent the interaction of a myosin-adenosine nucleotide complex with the actin-containing thin filament. Subsequently, Ashiba et al. reported that the steady-state ATPase of molluscan myosin exhibits a limited degree of Ca2+ activation in the absence of actin. Recently, however, we have shown that steady-state ATPase activity in relaxing conditions is dominated by the unregulated molecules in the myosin preparation. Single-turnover kinetic methods are required to monitor the highly suppressed ATPase activity of the regulated population. Using the latter approach, we report here that scallop myosin ATPase is reduced about 100-fold on removal of Ca2+. The regulatory light chains maintain the relaxed state via conformational changes which suppress the product release steps, irrespective of the presence of actin.     

Synthesis of Chiral Sulfoxides and Application in Enantioselective Allylation of Aldehydes with Allyltrichlorosilane

1 Results The enantioselective addition of allylic organometallic reagents to aldehydes is a fundamental tool in organic synthesis.The high degree of both diastereo-and enantioselectivity gives the possibility to obtain a wide series of homoallylic alcohols,versatile intermediates in a great number of synthesis[1]. One of the most successful approaches is related to the discovery that organocatalytic activation of the nucleophilic allyltrichlorosilanes by means of neutral Lewis bases,such as formamides,...     

Myeloid leukaemia inhibitory factor maintains the developmental potential of embryonic stem cells

Embryonic stem (ES) cells, the totipotent outgrowths of blastocysts, can be cultured and manipulated in vitro and then returned to the embryonic environment where they develop normally and can contribute to all cell lineages. Maintenance of the stem-cell phenotype in vitro requires the presence of a feeder layer of fibroblasts or of a soluble factor, differentiation inhibitory activity (DIA) produced by a number of sources; in the absence of DIA the ES cells differentiate into a wide variety of cell types. We recently noted several similarities between partially purified DIA and a haemopoietic regulator, myeloid leukaemia inhibitory factor (LIF), a molecule which induces differentiation in M1 myeloid leukaemic cells and which we have recently purified, cloned and characterized. We demonstrate here that purified, recombinant LIF can substitute for DIA in the maintenance of totipotent ES cell lines that retain the potential to form chimaeric mice.     

Coordination of circadian timing in mammals

Time in the biological sense is measured by cycles that range from milliseconds to years. Circadian rhythms, which measure time on a scale of 24 h, are generated by one of the most ubiquitous and well-studied timing systems. At the core of this timing mechanism is an intricate molecular mechanism that ticks away in many different tissues throughout the body. However, these independent rhythms are tamed by a master clock in the brain, which coordinates tissue-specific rhythms according to light input it receives from the outside world.     

Male development of chromosomally female mice transgenic for Sry

The initiation of male development in mammals requires one or more genes on the Y chromosome. A recently isolated gene, termed SRY in humans and Sry in mouse, has many of the genetic and biological properties expected of a Y-located testis-determining gene. It is now shown that Sry on a 14-kilobase genomic DNA fragment is sufficient to induce testis differentiation and subsequent male development when introduced into chromosomally female mouse embryos.     

Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.     

'Designer atoms' for quantum metrology

Entanglement is recognized as a key resource for quantum computation and quantum cryptography. For quantum metrology, the use of entangled states has been discussed and demonstrated as a means of improving the signal-to-noise ratio. In addition, entangled states have been used in experiments for efficient quantum state detection and for the measurement of scattering lengths. In quantum information processing, manipulation of individual quantum bits allows for the tailored design of specific states that are insensitive to the detrimental influences of an environment. Such 'decoherence-free subspaces' (ref. 10) protect quantum information and yield significantly enhanced coherence times. Here we use a decoherence-free subspace with specifically designed entangled states to demonstrate precision spectroscopy of a pair of trapped Ca+ ions; we obtain the electric quadrupole moment, which is of use for frequency standard applications. We find that entangled states are not only useful for enhancing the signal-to-noise ratio in frequency measurements--a suitably designed pair of atoms also allows clock measurements in the presence of strong technical noise. Our technique makes explicit use of non-locality as an entanglement property and provides an approach for 'designed' quantum metrology.     

Soil fertility limits carbon sequestration by forest ecosystems in a CO2-enriched atmosphere

Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, where tree growth is often limited by nutrient supply, in particular nitrogen. Here we present evidence that estimates of increases in carbon sequestration of forests, which is expected to partially compensate for increasing CO2 in the atmosphere, are unduly optimistic. In two forest experiments on maturing pines exposed to elevated atmospheric CO2, the CO2-induced biomass carbon increment without added nutrients was undetectable at a nutritionally poor site, and the stimulation at a nutritionally moderate site was transient, stabilizing at a marginal gain after three years. However, a large synergistic gain from higher CO2 and nutrients was detected with nutrients added. This gain was even larger at the poor site (threefold higher than the expected additive effect) than at the moderate site (twofold higher). Thus, fertility can restrain the response of wood carbon sequestration to increased atmospheric CO2. Assessment of future carbon sequestration should consider the limitations imposed by soil fertility, as well as interactions with nitrogen deposition.