Different activation energies in glucose uptake in Saccharomyces cerevisiae DFY1 suggest two transport systems

AbstractThe analysis of initial glucose uptake in Saccharomyces cerevisiae at 25°, 20°, 15° and 10°C by computer-assisted nonlinear regression analysis predicts two transport systems. The first demonstrates Michaelis–Menten kinetics and the second shows first order behaviour. The activation energies of these two systems were calculated by the Arrhenius equation at four different growth phases, namely early exponential (EE), middle exponential (ME2), late exponential (LE) and early stationary (ES) with 2% glucose in the batch medium. The activation energies calculated from the Vm values in EE, ME, LE and ES growth phases were 15.8±1.7, 13.5±1.0, 15.1±0.8 and 13.5±0.7 kcal/mol. These values are in agreement with activation energies calculated for the first mechanism, facilitated diffusion, which is the mechanism deduced from countertransport experiments. The activation energies derived for the second transport system from the first order rate constants in cells grown to EE, ME2, LE and ES were 8.0±2.1, 8.1±1.3, 9.6±3.0 and 7.5±2.6 kcal/mol. These values are still significantly higher than for free diffusion of glucose in water and lower as predicted for passage of glucose through the lipid phase. Therefore, we assume in addition to carrier-mediated facilitated diffusion the entrance of glucose into the cell through a pore

Planck early results XIV : ERCSC validation and extreme radio sources

Peer reviewe

Planck early results XV : Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources

Peer reviewe

The Theory of Brown Dwarfs and Extrasolar Giant Planets

Straddling the traditional realms of the planets and the stars, objects below the edge of the main sequence have such unique properties, and are being discovered in such quantities, that one can rightly claim that a new field at the interface of planetary science and and astronomy is being born. In this review, we explore the essential elements of the theory of brown dwarfs and giant planets, as well as of the new spectroscopic classes L and T. To this end, we describe their evolution, spectra, atmospheric compositions, chemistry, physics, and nuclear phases and explain the basic systematics of substellar-mass objects across three orders of magnitude in both mass and age and a factor of 30 in effective temperature. Moreover, we discuss the distinctive features of those extrasolar giant planets that are irradiated by a central primary, in particular their reflection spectra, albedos, and transits. Aspects of the latest theory of Jupiter and Saturn are also presented. Throughout, we highlight the effects of condensates, clouds, molecular abundances, and molecular/atomic opacities in brown dwarf and giant planet atmospheres and summarize the resulting spectral diagnostics. Where possible, the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for publication in the Reviews of Modern Physics. 30 figures are color. Most of the figures are in GIF format to reduce the overall size. The full version with figures can also be found at: http://jupiter.as.arizona.edu/~burrows/papers/rm

Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources

Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources, based on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multifrequency data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual shocks, each in their own phase of development, shape the radio spectra as they move in the relativistic jet. The SEDs presented in this paper were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed, with an emphasis on proper, physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shocks. Furthermore in many cases the Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission

Freshwater ostracodes in Quaternary permafrost deposits from the Siberian Arctic

Ostracode analysis was carried out on samples from ice-rich permafrost deposits obtained on the BykovskyPeninsula (Laptev Sea).A composite pro file was investigated that covers most of a 38-m thick permafrostsequence and corresponds to the last ca.60 kyr of the Late Quaternary.The ostracode assemblages aresimilar to those known from European Quaternary lake deposits during cold stages.The ostracode habitatswere small,shallow,cold,oligotrophic pools located in low centred ice wedge polygons or in small ther-mokarst depressions.In total,15 taxa,representing 7 genera,were identi fied from 65 samples.The studiedsection is subdivided into six ostracode zones that correspond to Late Quaternary climatic and environ-mental stadial-interstadial variations established by other paleoenvironmental proxies:(1)cold and dryZyrianian stadial (58 53 kyr BP);(2)warm and dry Karginian interstadial (48 34 kyr BP);(3)transitionfrom the Karginian interstadial to the cold and dry Sartanian stadial (34 21 kyr BP);(4)transition fromthe Sartanian stadial to the warm and dry Late Pleistocene period,the Allerød (21 14 kyr BP);(5)transition from the Allerød to the warm and wet Middle Holocene (14 7 kyr BP);and (6)cool and wetLate Holocene (ca.3 kyr BP).The abundance and diversity of the ostracodes will be used as an additionalbioindicator for paleoenvironmental reconstructions of the Siberian Arctic