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81.
Identification of NADPH:protochlorophyllide oxidoreductases A and B: a branched pathway for light-dependent chlorophyll biosynthesis in Arabidopsis thaliana. 总被引:10,自引:1,他引:9
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Illumination releases the arrest in chlorophyll (Chl) biosynthesis in etiolated angiosperm seedlings through the enzymatic photoreduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide), the first light-dependent step in chloroplast biogenesis. NADPH: Pchlide oxidoreductase (POR, EC 1.3.1.33), a nuclear-encoded plastid-localized enzyme, mediates this unique photoreduction. Paradoxically, light also triggers a drastic decrease in the amounts of POR activity and protein before the Chl accumulation rate reaches its maximum during greening. While investigating this seeming contradiction, we identified two distinct Arabidopsis thaliana genes encoding POR, in contrast to previous reports of only one gene in angiosperms. The genes, designated PorA and PorB, by analogy to the principal members of the phytochrome photoreceptor gene family, display dramatically different patterns of light and developmental regulation. PorA mRNA disappears within the first 4 h of greening, whereas PorB mRNA persists even after 16 h of illumination, mirroring the behavior of two distinct POR protein species. Experiments designed to help define the functions of POR A and POR B demonstrate exclusive expression of PorA in young seedlings and of PorB both in seedlings and in adult plants. Accordingly, we propose the existence of a branched light-dependent Chl biosynthesis pathway in which POR A performs a specialized function restricted to the initial stages of greening and POR B maintains Chl levels throughout angiosperm development. 相似文献
82.
The catalytic domains of murine Golgi alpha1,2-mannosidases IA and IB that
are involved in N-glycan processing were expressed as secreted proteins in
P.pastoris . Recombinant mannosidases IA and IB both required divalent
cations for activity, were inhibited by deoxymannojirimycin and
kifunensine, and exhibited similar catalytic constants using
Manalpha1,2Manalpha-O-CH3as substrate. Mannosidase IA was purified as a 50
kDa catalytically active soluble fragment and shown to be an inverting
glycosidase. Recombinant mannosidases IA and IB were used to cleave
Man9GlcNAc and the isomers produced were identified by high performance
liquid chromatography and proton-nuclear magnetic resonance spectroscopy.
Man9GlcNAc was rapidly cleaved by both enzymes to Man6GlcNAc, followed by a
much slower conversion to Man5GlcNAc. The same isomers of Man7GlcNAc and
Man6GlcNAc were produced by both enzymes but different isomers of
Man8GlcNAc were formed. When Man8GlcNAc (Man8B isomer) was used as
substrate, rapid conversion to Man5GlcNAc was observed, and the same
oligosaccharide isomer intermediates were formed by both enzymes. These
results combined with proton-nuclear magnetic resonance spectroscopy data
demonstrate that it is the terminal alpha1, 2-mannose residue missing in
the Man8B isomer that is cleaved from Man9GlcNAc at a much slower rate.
When rat liver endoplasmic reticulum membrane extracts were incubated with
Man9GlcNAc2, Man8GlcNAc2was the major product and Man8B was the major
isomer. In contrast, rat liver Golgi membranes rapidly cleaved
Man9GlcNAc2to Man6GlcNAc2and more slowly to Man5GlcNAc2. In this case all
three isomers of Man8GlcNAc2were formed as intermediates, but a distinctive
isomer, Man8A, was predominant. Antiserum to recombinant mannosidase IA
immunoprecipitated an enzyme from Golgi extracts with the same specificity
as recombinant mannosidase IA. These immunodepleted membranes were enriched
in a Man9GlcNAc2to Man8GlcNAc2- cleaving activity forming predominantly the
Man8B isomer. These results suggest that mannosidases IA and IB in Golgi
membranes prefer the Man8B isomer generated by a complementary mannosidase
that removes a single mannose from Man9GlcNAc2.
相似文献
83.
Zusammenfassung In den Langerhansschen Inseln der Ente fällt die histochemische Reaktion auf Zink nach vitaler intravenöser Injektion von Dithizon stark positiv aus. Die überwiegend aus B-Zellen bestehenden hellen Inseln und die fast nur aus A-Zellen bestehenden dunklen Inseln erlauben den Ausfall der Reaktion und die Lokalisation des Zinkdithizonates innerhalb der Inselzellen in beiden Inselzelltypen getrennt zu beurteilen. Zinkdithizonat in granulärer Form findet sich sowohl in den A-Zellen als auch in den B-Zellen. Es ist in ersteren violettrot, in letzteren karminrot. In den A-Zellen deckt sich bei intravitaler Reaktion das Zinkvorkommen nicht mit den -Granula. Am nativen Gefrierschnitt ist das Metalldithizonat beim Zinknachweis nicht granulär, sondern diffus im ganzen Cytoplasma nachzuweisen. Das gleiche gilt für die B-Zellen. Die beiden Methoden haben lokalisatorisch einen verschiedenen Effekt. In beiden Zelltypen der Inseln wird außer dem roten Zinkdithizonat eine schüttere schwarze Körnelung gefunden, die möglicherweise das Vorhandensein eines weiteren Schwermetalles anzeigt. Das Vogelpankreas eignet sich in besonderem Maße für Untersuchungen, welche den Zinkgehalt der A-Zellen im Zusammenhang mit dem Kohlenhydratstoffwechsel betreffen.Mit Unterstützung der Research Corporation, New York. 相似文献
84.
Runge SW Shelton KR Melton SA Moran WM 《Journal of biochemical and biophysical methods》2005,64(3):200-206
This paper reports the results of a series of experiments designed to test conditions that would permit NaCl to diffuse through 100 Da molecular weight cut-off (MWCO) and 1,000 Da MWCO membranes. For the 100 Da MWCO membrane, the membrane becomes completely impermeable to NaCl when dialyzed against distilled water (DW), but inclusion of one of a variety of different salts in the dialyzing solution maintains membrane permeability to NaCl. A titration experiment revealed that a minimum concentration of 0.1 mM of a salt such as KH2PO4 is required to sustain membrane permeability. In contrast, diffusion through the 1,000 Da MWCO membrane was slightly higher when DW was used as the dialysate. We conclude that the 100 Da MWCO membrane works well for a variety of dialysis applications provided that a maintenance salt is included in all dialyzing solutions. 相似文献
85.
Keeton RA Runge SW Moran WM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2004,174(2):129-138
We used the Aplysia californica intestinal epithelium to investigate the effect of alanine-stimulated Na+ absorption on apical membrane exocytosis and whether stimulated exocytosis requires intact actin filaments. The fluid-phase marker fluorescein dextran was used to determine rates of apical membrane exocytosis. L-alanine significantly increased apical exocytosis by ~30% compared to controls, and there is a modest, positive correlation between alanine-stimulated exocytosis and short-circuit current (I
SC). Thus, apical exocytosis is modulated to some extent by the magnitude of Na+ and alanine entry across the apical membrane. Apical exocytosis is also responsive to virtually any increase in Na+ and alanine entry because increments in alanine-stimulated I
SC as small as 1 A/cm2 stimulated exocytosis. We used D-alanine to determine which parameter (sensitivity to transport vs. magnitude of transport) was most important in activation of apical exocytosis. D-alanine-stimulated I
SC was one-sixth that of L-alanine, but stimulated exocytosis was only 29% less than that of L-alanine. Therefore, the apical exocytic system is more responsive to small increases in transport than to the magnitude of transport. Latrunculin A (Lat-A) disrupts the actin cytoskeleton and reduced constitutive apical exocytosis by ~65% and completely abolished alanine-stimulated exocytosis. Hence, constitutive exocytosis and alanine-stimulated exocytosis require actin filaments for recruitment of vesicles to the apical membrane. During nutrient absorption, actin filament-regulated apical exocytosis may represent a negative feedback system that modulates apical membrane tension.Abbreviations
alaASW
ASW containing alanine
-
C
m
membrane capacitance
-
ASW
artificial seawater
-
ETOH
ethanol
-
fCa
apical membrane fractional capacitance
-
FD
fluorescein dextran
-
G
K
plasma membrane potassium conductance
-
G
K,a
apical membrane potassium conductance
-
HRP
horseradish peroxidase
-
I
SC
short-circuit current
-
J
Na
transcellular net sodium flux
-
K
D
dissociation constant
-
Lat-A
latrunculin A
-
manASW
ASW containing mannitol
-
PT
proximal tubule
-
RFU
relative fluorescence units
-
V
a
apical membrane potential
Communicated by L.C.-H. Wang 相似文献
86.
Young CG Knight CA Vickers KC Westbrook D Madamanchi NR Runge MS Ischiropoulos H Ballinger SW 《American journal of physiology. Heart and circulatory physiology》2005,288(4):H1683-H1689
Routine exercise is widely recognized as cardioprotective. Exercise induces a variety of effects within the cardiovasculature, including decreased mitochondrial damage and improved aerobic capacity. It has been generally thought that the transient increase in oxidative stress associated with exercise initiates cardioprotective processes. Somewhat paradoxically, increased oxidative stress associated with cardiovascular disease (CVD) risk factors is thought to play an important role in the promotion and development of CVD. Hence, it is possible that CVD risk factors that increase oxidative stress (e.g., hypercholesterolemia) may modulate the cardioprotective effects of exercise. In this regard, the interaction between CVD risk factors and exercise on atherosclerotic lesion development and basal oxidant load is less defined. To determine the influence of preexistent hypercholesterolemia on cardioprotective effects of exercise, atherosclerotic lesion formation, oxidant load, mitochondrial damage, protein nitration (3-nitrotyrosine levels), and mitochondrial enzyme activities were determined in aortic tissues from normocholesterolemic (C57 control) and hypercholesterolemic [apoliprotein E-deficient (apoE(-/-))] mice after 16 wk of regular exercise. In normocholesterolemic mice, regular exercise was associated with decreased mitochondrial damage and oxidant load and increased SOD2 and adenine nucleotide translocator activities. Exercise did not decrease endogenous oxidant load and mitochondrial damage in hypercholesterolemic mice and did not reduce atherosclerotic lesion development. These data are consistent with the notion that CVD risk factors associated with increased oxidative stress can alter the benefits of exercise and that mitochondrial damage appears to be correlated with the cardiovascular effects of exercise. 相似文献
87.
Estimating the per‐capita contribution of habitats and pathways in a migratory network: a modelling approach
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Ruscena Wiederholt Brady J. Mattsson Wayne E. Thogmartin Michael C. Runge Jay E. Diffendorfer Richard A. Erickson Paula Federico Laura López‐Hoffman John M. Fryxell D. Ryan Norris Christine Sample 《Ecography》2018,41(5):815-824
Every year, migratory species undertake seasonal movements along different pathways between discrete regions and habitats. The ability to assess the relative demographic contributions of these different habitats and pathways to the species’ overall population dynamics is critical for understanding the ecology of migratory species, and also has practical applications for management and conservation. Metrics for assessing habitat contributions have been well‐developed for metapopulations, but an equivalent metric is not currently available for migratory populations. Here, we develop a framework for estimating the demographic contributions of the discrete habitats and pathways used by migratory species throughout the annual cycle by estimating the per capita contribution of cohorts using these locations. Our framework accounts for seasonal movements between multiple breeding and non‐breeding habitats and for both resident and migratory cohorts. We illustrate our framework using a hypothetical migratory network of four habitats, which allows us to better understand how variations in habitat quality affect per capita contributions. Results indicate that per capita contributions for any habitat or pathway are dependent on habitat‐specific survival probabilities in all other areas used as part of the migratory circuit, and that contribution metrics are spatially linked (e.g. reduced survival in one habitat also decreases the contribution metric for other habitats). Our framework expands existing theory on the dynamics of spatiotemporally structured populations by developing a generalized approach to estimate the habitat‐ and pathway‐specific contributions of species migrating between multiple breeding and multiple non‐breeding habitats for a range of life histories or migratory strategies. Most importantly, it provides a means of prioritizing conservation efforts towards those migratory pathways and habitats that are most critical for the population viability of migratory species. 相似文献
88.
Nicholas R. Record Rubao Ji Frédéric Maps Øystein Varpe Jeffrey A. Runge Colleen M. Petrik David Johns 《Journal of Biogeography》2018,45(10):2238-2251
Aim
One of the primary characteristics that determines the structure and function of marine food webs is the utilization and prominence of energy‐rich lipids. The biogeographical pattern of lipids throughout the ocean delineates the marine “lipidscape,” which supports lipid‐rich fish, mammal, and seabird communities. While the importance of lipids is well appreciated, there are no synoptic measurements or biogeographical estimates of the marine lipidscape. Productive lipid‐rich food webs in the pelagic ocean depend on the critical diapause stage of large pelagic copepods, which integrate lipid production from phytoplankton, concentrating it in space and time, and making it available to upper trophic levels as particularly energy‐rich wax esters. As an important first step towards mapping the marine lipidscape, we compared four different modelling approaches of copepodid diapause, each representing different underlying hypotheses, and evaluated them against global datasets.Location
Global Ocean.Taxon
Copepoda.Methods
Through a series of global model runs and data comparisons, we demonstrated the potential for regional studies to be extended to estimate global biogeographical patterns of diapause. We compared four modelling approaches each designed from a different perspective: life history, physiology, trait‐based community ecology, and empirical relationships. We compared the resulting biogeographical patterns and evaluated the model results against global measurements of copepodid diapause.Results
Models were able to resolve more than just the latitudinal pattern of diapause (i.e. increased diapause prevalence near the poles), but to also pick up a diversity of regions where diapause occurs, such as coastal upwelling zones and seasonal seas. The life history model provided the best match to global observations. The predicted global biogeographical patterns, combined with carbon flux estimates, suggested a lower bound of 0.031–0.25 Pg C yr?1 of downward flux associated with copepodid diapause.Main conclusions
Results indicated a promising path forward for representing a detailed biogeography of the marine lipidscape and its associated carbon flux in global ecosystem and climate models. While complex models may offer advantages in terms of reproducing details of community structure, simpler theoretically based models appeared to best reproduce broad‐scale biogeographical patterns and showed the best correlation with observed biogeographical patterns.89.
C Bode M S Runge J B Newell G R Matsueda E Haber 《The Journal of biological chemistry》1987,262(22):10819-10823
The plasminogen activator urokinase was linked covalently to a monoclonal antibody specific for the amino terminus of the beta chain of human fibrin by means of the unidirectional cross-linking reagent N-succinimidyl-3-(2-pyridyldithio)propionate. N-Succinimidyl-3-(2-pyridyldithio)propionate allowed the amino groups on urokinase to be coupled to the sulfhydryl groups on iminothiolane (which had been introduced into the antibody before the coupling reaction). The inter-heavy chain sulfhydryl of the Fab' of this antibody was also linked to N-succinimidyl-3-(2-pyridyldithio)propionate-substituted urokinase. The antibody- or Fab'-urokinase complexes were purified by two affinity chromatography steps. In the first, benzamidine was used as ligand for urokinase, in the second, a heptapeptide consisting of the 7 amino-terminal residues of the beta chain of fibrin (beta peptide) was used as ligand for the antibody. The activity of the purified conjugates was compared with that of urokinase alone in an assay measuring lysis of 125I-fibrin monomer covalently linked to Sepharose CL-4B. For any concentration of either urokinase alone or urokinase-antifibrin antibody conjugate, an equivalent amount of lysis (release of labeled peptide from fibrin monomer-Sepharose) was obtained with 1/250 the concentration (with respect to urokinase content) of antifibrin antibody-urokinase conjugate. The antifibrin Fab'-urokinase conjugate exhibited a similar enhancement of activity in comparison with urokinase. Enhanced fibrinolysis was fully inhibited by beta peptide. These results suggest that antibody targeting enhances the concentration of urokinase in the vicinity of immobilized fibrin monomer, thereby also increasing the local conversion of plasminogen to plasmin, which in turn degrades its substrate, fibrin. Univalent antigen-antibody binding is sufficient for optimal efficiency. 相似文献
90.
Heribert Gras Michael Hörner Lars Runge Friedrich-Wilhelm Schürmann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1990,166(6):901-914
Summary Responses to sensory stimuli and spike activity uring walking were investigated in bilaterally symmetrical dorsal unpaired median (DUM) neurons of the cricket. Intracellular recordings within the prothoracic ganglion were made either in restrained animals or in stationary walking specimens whilst parameters of their intended locomotion were measured. Three types of DUM cells were distinguished morphologically and physiologically. DUMa neurons send axons through segmental nerves. They often generated spontaneously large action potentials with low frequencies. Most DUMa neurons showed multimodal sensitivity, preferentially to cereal wind puffs and 15 kHz sound. Mean latencies ranged from 25 to 349 ms. Their large intraindividual variability could be correlated with behavioral modes during walking. Generally, the spike frequency increased with increased forward speed, while it was not related to turning. DUMb neurons projected either through the anterior or posterior connectives, but seemed physiologically similar to DUMa neurons. DUMc neurons were H-shaped with axons in both pairs of connectives. No external stimulus led to discrete spikes, but the regular spontaneous activity was modulated following cereal wind puffs to a restrained animal. During wind evoked escape the spike activity of another DUMc cell was modulated in phase with the rhythmic running behavior. The possibly different functions of DUMa and DUMc neurons during walking are discussed. 相似文献