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61.
62.
Physiological optimization underlies growth rate-independent chlorophyll-specific gross and net primary production 总被引:1,自引:0,他引:1
Kimberly H. Halsey Allen J. Milligan Michael J. Behrenfeld 《Photosynthesis research》2010,103(2):125-137
Characterization of physiological variability in phytoplankton photosynthetic efficiencies is one of the greatest challenges
in assessing ocean net primary production (NPP) from remote sensing of surface chlorophyll (Chl). Nutrient limitation strongly influences phytoplankton intracellular pigmentation,
but its impact on Chl-specific NPP (NPP
*) is debated. We monitored six indices of photosynthetic activity in steady-state Dunaliella tertiolecta cultures over a range of nitrate-limited growth rates (μ), including photosynthetic efficiency of PSII (F
v/F
m), O2-based gross and net production, 20 min and 24 h carbon assimilation, and carbon- and μ-based NPP. Across all growth rates, O2-based Chl-specific gross primary production (
GPP\textO2 * GPP_{{{\text{O}}_{2} }}^{*} ), NPP
*, and F
v/F
m were constant.
GPP\textO2 * GPP_{{{\text{O}}_{2} }}^{*} was 3.3 times greater than NPP
*. In stark contrast, Chl-specific short-term C fixation showed clear linear dependence on μ, reflecting differential allocation
of photosynthate between short-lived C products and longer-term storage products. Indeed, 14C incorporation into carbohydrates was five times greater in cells growing at 1.2 day−1 than 0.12 day−1. These storage products are catabolized for ATP and reductant generation within the period of a cell cycle. The relationship
between Chl-specific gross and net O2 production, short-term 14C-uptake, NPP
*, and growth rate reflects cellular-level regulation of fundamental metabolic pathways in response to nutrient limitation.
We conclude that growth rate-dependent photosynthate metabolism bridges the gap between gross and net production and resolves
a controversial question regarding nutrient limitation effects on primary production measures. 相似文献
63.
The extent and ecological significance of trophic linkages across ecosystem boundaries have been the subject of considerable recent research attention. North American beavers Castor canadensis engineer terrestrial influences in aquatic ecosystems by constructing terrestrial food caches near their lodges and aquatic influences in terrestrial ecosystems by building dams and flooding low lying areas. However, it is poorly resolved to what extent beavers rely on aquatic food sources and whether this reliance is greater during winter when ice cover physically confines beavers to aquatic habitats or during summer when warm, ice free water promotes the growth and accessibility of aquatic vegetation. Working in a subarctic region, we surveyed the abundance of aquatic and terrestrial food sources in and around lotic and lentic environments and estimated their contributions to beaver diets during open water and ice covered periods using carbon and nitrogen stable isotope analysis of hair samples. Ponds had four times more aquatic vegetation than streams, but terrestrial habitats around ponds had less than half as much shrub cover as habitats adjacent to streams. Beaver diets in this subarctic environment are estimated to be comprised of 60 to 80% aquatic vegetation, with beavers occupying ponds consuming more aquatic vegetation in winter than beavers occupying streams, which rely more on terrestrial shrubs cached near their lodge. Collectively, these results show how the influence of physical barriers on ecosystem linkages can be modified by habitat‐ and season‐specific abundances of preferred resources and the potential for animals to consume food in ecosystems and seasons different from where and when the food was harvested. 相似文献
64.
65.
Early resolution of herpes simplex virus type 2 infection of the murine genital tract involves stimulation of genital parenchymal cells by gamma interferon 下载免费PDF全文
Early clearance of a thymidine kinase-deficient strain of herpes simplex virus type 2 from the female genital tract required T-cell-produced gamma interferon (IFN-gamma). Transfer of activated CD8+ T cells to irradiated C57BL/6 mice resulted in rapid virus clearance, but clearance was greatly delayed in recipients deficient in the IFN-gamma receptor (IFN-gammaR). Early virus clearance was demonstrated in radiation chimeras in which IFN-gammaR expression was limited to parenchymal cells, but resolution was significantly delayed in chimeras deficient in IFN-gammaR expression and chimeras expressing IFN-gammaR only on hematopoietic cells. Together, these results suggest that early IFN-gamma-mediated protection was manifested mainly by stimulation of genital parenchymal cells. 相似文献
66.
Clizbe DB Owens ML Masuda KR Shackelford JE Krisans SK 《The Journal of biological chemistry》2007,282(9):6668-6676
We recently described the identification of a novel isopentenyl diphosphate isomerase, IDI2 in humans and mice. Our current data indicate that, in humans, IDI2 is expressed only in skeletal muscle. Expression constructs of human IDI2 in Saccharomyces cerevisiae can complement isomerase function in an idi1-deficient yeast strain. Furthermore, IDI2 has the ability to catalyze the isomerization of [(14)C]IPP to [(14)C]DMAPP. Enzyme kinetic analysis of partially purified IDI2 demonstrate the novel isozyme has a maximal relative specific activity of 1.2 x 10(-1) +/- 0.3 micromol min(-1) mg(-1) at pH 8.0 with a K(IPP)(m) value of 22.8 microm IPP. Both isozymes, IDI1 and IDI2 are localized to the peroxisome by a PTS1-dependent pathway. Finally, our data suggest that IDI2 is regulated independently from IDI1, by a mechanism that may involve PPARalpha. 相似文献
67.
The alanine racemase of Mycobacterium smegmatis is essential for growth in the absence of D-alanine 下载免费PDF全文
Alanine racemase, encoded by the gene alr, is an important enzyme in the synthesis of d-alanine for peptidoglycan biosynthesis. Strains of Mycobacterium smegmatis with a deletion mutation of the alr gene were found to require d-alanine for growth in both rich and minimal media. This indicates that alanine racemase is the only source of d-alanine for cell wall biosynthesis in M. smegmatis and confirms alanine racemase as a viable target gene for antimycobacterial drug development. 相似文献
68.
Three-dimensional reconstruction of bovine brain V-ATPase by cryo-electron microscopy and single particle analysis 总被引:1,自引:0,他引:1
Bovine V-ATPase from brain clathrin-coated vesicles was investigated by cryo-electron microscopy and single particle analysis. Our studies revealed great flexibility of the central linker region connecting V1 and V0. As a consequence, the two sub-complexes were processed separately and the resulting volumes were merged computationally. We present the first three-dimensional (3D) map of a V-ATPase obtained from cryo-electron micrographs. The overall resolution was estimated 34 Å by Fourier shell correlation (0.5 cutoff). Our 3D reconstruction shows a large peripheral stalk and a smaller, isolated peripheral density, suggesting a second, less well-resolved peripheral connection. The 3D map reveals new features of the large peripheral stator and of the collar-like density attached to the membrane domain. Our analyses of the membrane domain indicate the presence of six proteolipid subunits. In addition, we could localize the V0 subunit a flanking the large peripheral stalk. 相似文献
69.
Schalk-Hihi C Schubert C Alexander R Bayoumy S Clemente JC Deckman I DesJarlais RL Dzordzorme KC Flores CM Grasberger B Kranz JK Lewandowski F Liu L Ma H Maguire D Macielag MJ McDonnell ME Mezzasalma Haarlander T Miller R Milligan C Reynolds C Kuo LC 《Protein science : a publication of the Protein Society》2011,20(4):670-683
A high-resolution structure of a ligand-bound, soluble form of human monoglyceride lipase (MGL) is presented. The structure highlights a novel conformation of the regulatory lid-domain present in the lipase family as well as the binding mode of a pharmaceutically relevant reversible inhibitor. Analysis of the structure lacking the inhibitor indicates that the closed conformation can accommodate the native substrate 2-arachidonoyl glycerol. A model is proposed in which MGL undergoes conformational and electrostatic changes during the catalytic cycle ultimately resulting in its dissociation from the membrane upon completion of the cycle. In addition, the study outlines a successful approach to transform membrane associated proteins, which tend to aggregate upon purification, into a monomeric and soluble form. 相似文献
70.
Cairns M Ghani A Okell L Gosling R Carneiro I Anto F Asoala V Owusu-Agyei S Greenwood B Chandramohan D Milligan P 《PloS one》2011,6(4):e18947