Activation of M-phase-specific histone H1 kinase by modification of the phosphorylation of its p34cdc2 and cyclin components

An M-phase-specific histone H1 kinase (H1K) has been described in a wide variety of eukaryotic cell types undergoing the G2/M transition in the cell division cycle. We have used p13suc1-Sepharose affinity chromatography to purify H1K to near homogeneity from matured starfish oocytes. A yield of 67% was obtained. Active H1K behaves as a 90- to 100-kD protein and appears to be constituted of equimolar amounts of cyclin and p34cdc2. The p34cdc2 subunit becomes tyrosine-dephosphorylated as the H1K is activated during entry of the oocytes into M phase, whereas the cyclin subunit is reciprocally phosphorylated. Acid phosphatase treatment of inactive p34cdc2/cyclin complex induces p34cdc2 dephosphorylation and three- to eightfold stimulation of the enzyme activity. These results suggest that active M-phase-specific H1K is constituted of both dephosphorylated p34cdc2 and phosphorylated cyclin

What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?

The ocean contributes to regulating atmospheric CO2 levels, partly via variability in the fraction of primary production (PP) which is exported out of the surface layer (i.e. the e-ratio). Southern Ocean studies have found that, contrary to global scale analyses, an inverse relationship exists between e-ratio and PP. This relationship remains unexplained, with potential hypotheses being i) large export of dissolved organic carbon (DOC) in high PP areas, ii) strong surface microbial recycling in high PP regions and/ or iii) grazing mediated export varies inversely with PP. We find that the export of DOC has a limited influence in setting the negative e-ratio/PP relationship. However, we observed that at sites with low PP and high e-ratios, zooplankton mediated export is large and surface microbial abundance low suggesting that both are important drivers of the magnitude of the e-ratio in the Southern Ocean

On estimates for the vertical nitrate flux due to eddy pumping

Integral tracer methods consistently imply an annual new primary production of 0.5 +/- 0.15 mol N m(-2) yr(-1) for the Sargasso Sea region of the North Atlantic. It has been suggested that as much as half of this may be fueled by the vertical nitrate flux associated with "eddy pumping.'' The key factor in estimates of eddy pumping is the relationship between the time for which water upwelled within eddies remains within the euphotic zone and the rate at which upwelled nutrients are consumed by phytoplankton. The uplift time is strongly influenced by the nature of the eddy, more specifically by its ability to trap waters within it as it propagates. We investigate two scenarios: If eddies propagate as nonlinear features, such that they retain the water within them for their lifetime, only a fraction of eddy "events'' observed at a fixed location actually contribute to the nitrate flux at that position; if eddies propagate as linear features, the efficiency of the pumping process, assumed in current altimetry-based estimates to be 100%, may be very significantly overestimated. Either scenario is shown to result in a major reduction in altimetry-based estimates of the vertical nitrate flux due to eddy pumping. Furthermore, the major contribution of local nitrification to the nitrate "recharging'' of previously uplifted waters, witnessed in our model, raises the possibility that much inferred new production in this area, based on nitrate uptake, is actually regenerated. Our results support the view that mesoscale eddy pumping may not be able to close the Sargasso Sea nitrate budge

Non-Redfield carbon and nitrogen cycling in the Sargasso Sea: pelagic imbalances and export flux

An ecosystem model embedded in a one-dimensional physical model is used to study the stoichiometry of carbon and nitrogen cycling at the Bermuda Atlantic Time Series site. The model successfully provides a budget for the processes contributing to the drawdown of dissolved inorganic carbon (DIC) that is observed in surface waters in the absence of detectable nitrate throughout much of the summer. The modeled drawdown is initially driven by export fueled by in situ N and accumulation of dissolved organic carbon, with continued DIC consumption after nutrient exhaustion resulting largely from nitrogen fixation and outgassing of CO2 to the atmosphere. The modeled export flux of organic C at 300 m is dominated by particles (81%), with a nevertheless significant fraction (19%) due to dissolved organic matter. The predicted combined C/N of particulate and dissolved export increases from 10.8 at 70 m to 14.3 at 300 m, because of preferential remineralization of N. In theory, at least as a first approximation, the ratio of net consumption of DIC and nutrients in the euphotic zone is equivalent to this C/N of export. However, the C/N of consumption during DIC drawdown averaged 23.5 (>10.8), indicating that this assumption is not always valid and C/N ratios of nutrient consumption cannot reliably be used to estimate the export ratio, which is difficult to measure directly. The work highlights the complex interplay between the cycling of C and N the upper ocean and the resultant export flux

Influence of consumer-driven nutrient recycling on primary production and the distribution of N and P in the ocean

Abstract. In this study we investigated the impact of consumer-driven nutrient recycling (CNR) on oceanic primary production and the distribution of nitrogen (N) and phosphorus (P) in the deep ocean. For this purpose, we used and extended two existing models: a 2-box model of N and P cycling in the global ocean (Tyrrell, 1999), and the model of Sterner (1990) which formalised the principles of CNR theory. The resulting model showed that marine herbivores may affect the supply and the stoichiometry of N and P in the ocean, thereby exerting a control on global primary production. The predicted global primary production was higher when herbivores were included in the model, particularly when these herbivores had higher N:P ratios than phytoplankton. This higher primary production was triggered by a low N:P resupply ratio, which, in turn, favoured the P-limited N2-fixation and eventually the N-limited non-fixers. Conversely, phytoplankton with higher N:P ratios increased herbivore yield until phosphorus became the limiting nutrient, thereby favouring herbivores with a low P-requirement. Finally, producer-consumer interactions fed back on the N and P inventories in the deep ocean through differential nutrient recycling. In this model, N deficit or N excess in the deep ocean resulted not only from the balance between N2-fixation and denitrification, but also from CNR, especially when the elemental composition of producers and consumers differed substantially. Although the model is fairly simply, these results emphasize our need for a better understanding of how consumers influence nutrient recycling in the ocean. </jats:p

Effects of an iron-light co-limitation on the elemental composition (Si, C, N) of the marine diatoms <I>Thalassiosira oceanica</I> and <I>Ditylum brightwellii</I>

We examined the effect of iron (Fe) and Fe-light (Fe-L) co-limitation on cellular silica (BSi), carbon (C) and nitrogen (N) in two marine diatoms, the small oceanic diatom Thalassiosira oceanica and the large coastal species Ditylum brightwellii. We showed that C and N per cell tend to decrease with increasing Fe limitation (i.e. decreasing growth rate), both under high light (HL) and low light (LL). We observed an increase (T. oceanica, LL), no change (T. oceanica, HL) and a decrease (D. brightwellii, HL and LL) in BSi per cell with increasing degree of limitation. The comparison with literature data showed that the trend in C and N per cell for other Fe limited diatoms was similar to ours. Interspecific differences in C and N quotas of Fe limited diatoms observed in the literature seem thus to be mostly due to variations in cell volume. On the contrary, there was no global trend in BSi per cell or per cell volume, which suggests that other interspecific differences than Fe-induced variations in cell volume influence the degree of silicification. The relative variations in C:N, Si:C and Si:N versus the relative variation in specific growth rate (i.e. μ:μmax) followed the same patterns for T. oceanica and D. brightwellii, whatever the irradiance level. However, the variations of C:N under Fe limitation reported in the literature for other diatoms are contrasted, which may thus be more related to growth conditions than to interspecific differences. As observed in other studies, Si:C and Si:N ratios increased by more than 2-fold between 100% and 40% of μmax. Under more severe limitation (HL and LL), we observed for the first time a decrease in these ratios. These results may have important biogeochemical implications on the understanding and the modelling of the oceanic biogeochemical cycles, e.g. carbon and silica export

Conformational Flexibility of a Human Immunoglobulin Light Chain Variable Domain by Relaxation Dispersion Nuclear Magnetic Resonance Spectroscopy: Implications for Protein Misfolding and Amyloid Assembly

Theprocess of conformational conversion of normally solubleproteins into large oligomeric aggregates and amyloid fibrils has been linked to over 40 human disease states.1,2 The most widespread systemic disease of this type in the Western Hemi-sphere, light-chain amyloidosis (AL), is associated with the deposition in organs and tissues, including kidneys, lymphatic vessels, and heart, of amyloid fibrils composed of immunoglo-bulin (Ig) light-chain variable domains (VL) of the λ or k family.3,4 It has previously been proposed that specific amino acid mutations to their germline sequences alter the thermo-dynamic stabilities of certain Ig VLs, predisposing them toward aggregation and amyloid formation in vivo.59 As suggested by comparative structural studies,1015 these pro-cesses are likely initiated by partial disruption of the native secondary, tertiary, and quaternary structure, a common motif encountered for numerous other amyloidogenic proteins,1,