Boron isotope sensitivity to seawater pH change in a species of Neogoniolithon coralline red alga

The increase in atmospheric carbon dioxide (CO2) observed since the industrial revolution has reduced surface ocean pH by ∼0.1 pH units, with further change in the oceanic system predicted in the coming decades. Calcareous organisms can be negatively affected by extreme changes in seawater pH (pHsw) such as this due to the associated changes in the oceanic carbonate system. The boron isotopic composition (δ11B) of biogenic carbonates has been previously used to monitor pH at the calcification site (pHcf) in scleractinian corals, providing mechanistic insights into coral biomineralisation and the impact of variable pHsw on this process. Motivated by these investigations, this study examines the δ11B of the high-Mg calcite skeleton of the coralline red alga Neogoniolithon sp. to constrain pHcf, and investigates how this taxon’s pHcf is impacted by ocean acidification. δ11B was measured in multiple algal replicates (n = 4–5) cultured at four different pCO2 scenarios – averaging (±1σ) 409 (±6), 606 (±7), 903 (±12) and 2856 (±54) μatm, corresponding to average pHsw (±1σ) of 8.19 (±0.03), 8.05 (±0.06), 7.91 (±0.03) and 7.49 (±0.02) respectively. Results show that skeletal δ11B is elevated relative to the δ11B of seawater borate at all pHsw treatments by up to 18‰. Although substantial variability in δ11B exists between replicate samples cultured at a given pHsw (smallest range = 2.32‰ at pHsw 8.19, largest range = 6.08‰ at pHsw 7.91), strong correlations are identified between δ11B and pHsw (R2 = 0.72, p < 0.0001, n = 16) and between δ11B and B/Ca (R2 = 0.72, p < 0.0001, n = 16). Assuming that skeletal δ11B reflects pHcf as previously observed for scleractinian corals, the average pHcf across all experiments was 1.20 pH units (0.79 to 1.56) higher than pHsw, with the magnitude of this offset varying parabolically with decreasing pHsw, with a maximum difference between pHsw and pHcf at a pHsw of 7.91. Observed relationships between pHsw and calcification rate, and between pHsw and pHcf, suggest that coralline algae exhibit some resilience to moderate ocean acidification via increase of pHcf relative to pHsw in a similar manner to scleractinian corals. However, these results also indicate that pHcf cannot be sufficiently increased by algae exposed to a larger reduction in pHsw, adversely impacting calcification rates of coralline red algae

Valeur des tests ergométriques de laboratoire pour le suivi de l'entraînement de triathlètes de haut niveau en période de préparation

Huonker M., Muller F.-M., Orschitt M., Keul Joseph. Valeur des tests ergométriques de laboratoire pour le suivi de l'entraînement de triathlètes de haut niveau en période de préparation. In: Les Cahiers de l'INSEP, n°20, 1997. Un sport, deux enchaînements, trois disciplines : le triathlon. Actes du 1er symposium international de l'entraînement en triathlon. pp. 105-109

Crystallization of human low density lipoprotein (LDL), a large lipid-protein complex : collection of X-ray data at very low resolution

Human LDL subfractions LDL-2 (d=1.031-1.034 g/ml) and LDL-5 (d=1.040-1.044 g/ml) were crystallized in different crystal forms using polyethylene glycol as a precipitant. Both fractions were from one donor. Crystals of LDL-5 were yellow, hexagonal, and showed no dichroism. Of LDL-2 two dichroitic crystal forms were obtained. One had a rod-like shape with deep notches at both ends (form A), the other was a more compact form with plain surfaces (form B). To be able to measure low order reflections down to 300 Å a special experimental setup was developed. One single crystal was used to obtain a complete native data set of LDL-2 (form A) with an overall internal R-factor of 4.5% for reflections from 100 to 28 Å. Data were collected under cryogenic conditions using synchrotron radiation. The space group is most probably C2 with unit cell dimensions of a=183 Å, b=421 Å, c=385 Å, α=γ=90°, β≈90°. Further optimization of the crystallization conditions and the search for heavy metal derivatives are in progress

Crystallization and Preliminary X-Ray Diffraction Data of Two Different Human Low-Density Lipoprotein (LDL) Subfractions

Human LDL subfractions LDL-2 (d = 1.031 1.034 g/ml) and LDL-5 (d = 1.040 1.044 g/ml) were crystallized in two different crystal forms by using polyethylene glycol as a precipitant. Both fractions were from one donor. Crystals of LDL-5 were yellow, hexagonal, and showed no dichroism. Crystals of LDL-2 were of the same color, had a rodlike shape with notches at both ends, and were highly dichroitic. LDL-2 crystals diffracted to a resolution of 29 Å by using synchrotron radiation. Indexing in P1 resulted in preliminary parameters for the reduced cell of a = 171 Å, b = 438 Å, c = 519 Å, α = 102°, β = 99°, γ = 91. These dimensions are consistent with the size of LDL particles. Using Fourier transform infrared spectroscopy (FTIR) and agarose gel electrophoresis, we could further confirm that the crystals consist of LDL. The FTIR spectrum showed bands characteristic for lipids and protein. Dissolved crystals exhibited a mobility similar to native LDL in agarose gels and could be stained with anti-human apolipoprotein B (apoB)