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221.
In etiolated barley (Hordeum vulgare L.) seedlings the light-induced accumulation of chlorophyll is controlled by two light-dependent NADPH-proto-chlorophyllide oxidoreductase (POR; EC 1.6.99.1) enzymes. While the concentration of one of these enzymes (POR A) and its mRNA rapidly decline during illumination, the second POR protein (POR B) and its mRNA remain at an approximately constant level during the transition from dark growth to the light. These results may suggest that only one of the enzymes, POR B, operates throughout the greening process and in light-adapted mature plants while the second enzyme, POR A, is active only in etiolated seedlings at the beginning of illumination. The fate of the two POR proteins and their mRNAs in fully green plants, however, has not been studied yet. In the present work we determined changes in the level of POR A and POR B proteins and mRNAs in green barley plants kept under a diurnal 12 h light/12 h dark cycle. In green barley plants, not only POR B is present but also trace amounts of POR A continue to reappear transiently at the end of a night period and seem to be involved in the synthesis and accumulation of chlorophyll at the beginning of each day.Abbreviations Chl
chlorophyll
- Chlide
chlorophyllide
- Lhcb
light-harvesting chlorophyll a/b protein
- Pchlide
protochlorophyllide
- POR
NADPH-protochlorophyllide oxidoreductase
Dedicated to Horst Senger on the occasion of his 65th birthday.We thank Dr. Dieter Rubli for photography and Renate Langjahr for typing. This work was supported by the Swiss National Science Foundation and the ETH-Zürich. 相似文献
222.
Maturation of the immune response in germinal centers. 总被引:79,自引:0,他引:79
Germinal centers develop in peripheral lymphatic tissue during the primary immune response and may play a crucial role in affinity maturation. We have compared the diversification of the antigen-specific repertoire of B cells, both from within and from outside the germinal centers, during the murine response to 2-phenyloxazolone (phOx). By sequencing V kappa Ox1 L-chains characteristic of phOx-specific antibodies, we show that somatic mutations accumulate in germinal center B cells and that a mutation conferring high affinity binding is found with increasing frequency. An analysis of V/D/J rearrangements suggests that this mutation occurred independently in many B cells, which were then preferentially expanded. We conclude that, although the hypermutation mechanism may be activated before germinal centers develop, affinity maturation by hypermutation and selection takes place in the germinal centers. 相似文献
223.
224.
Effect of light on the NADPH-protochlorophyllide oxidoreductase of Arabidopsis thaliana 总被引:4,自引:0,他引:4
A cDNA encoding the NADPH-protochlorophyllide oxidoreductase (Pchlide reductase) of Arabidopsis thaliana has been isolated and sequenced. The cDNA contains the complete reading frame for the precursor of the Pchlide reductase. The deduced amino acid sequence of the Arabidopsis enzyme closely resembles the corresponding sequences of barley and oat. The cDNA has been used as a template for the synthesis of the enzyme protein in Escherichia coli. An antiserum was raised against this enzyme protein and both the antiserum and the cDNA were used as experimental tools to study the effects of light on the Pchlide reductase in A. thaliana.When etiolated seedlings of Arabidopsis were exposed to light the enzyme activity and the concentration of the enzyme protein rapidly declined. Similar light effects have been described previously for other angiosperms. In contrast to most of these species, however, in Arabidopsis only minor changes in Pchlide reductase mRNA content could be observed when etiolated seedlings were exposed to light. 相似文献
225.
A soluble form of bovine rod photoreceptor phosphodiesterase has a novel 15-kDa subunit 总被引:1,自引:0,他引:1
P G Gillespie R K Prusti E D Apel J A Beavo 《The Journal of biological chemistry》1989,264(21):12187-12193
A substantial fraction (20-30%) of the bovine rod outer segment phosphodiesterase (PDE) activity is not associated with outer segment membranes prepared with buffers of moderate ionic strength; this PDE activity appears to represent a distinct, soluble isozyme. Although this PDE isozyme can be demonstrated to be present in sealed rod outer segments, it is discarded from most standard rod outer segment preparations. A method was developed that allowed the rapid purification of the soluble rod PDE by 2600-fold, to apparent homogeneity, using a monoclonal antibody column (ROS-1a). The soluble rod PDE isozyme has a novel Mr = 15,000 subunit (delta) in addition to subunits of Mr = 88,000 (alpha sol), 84,000 (beta sol), and 11,000 (gamma sol). The delta subunit comigrates with and may be identical to the cone PDE 15-kDa subunit. The small subunits of the soluble rod PDE and the membrane-associated rod PDE were isolated by reverse-phase chromatography. The gamma sol subunit was a potent inhibitor of trypsin-activated rod PDE, inhibiting 50% of 1 pM PDE activity at a concentration of 11 pM. This concentration was similar to that observed for the gamma subunit of the membrane-associated rod PDE. The purified delta subunit did not appear to affect PDE activity; this subunit was, however, unusually difficult to keep in solution. All of the kinetic and physical properties of the soluble rod PDE tested thus far are similar to those of the membrane-associated form, except for the presence of the delta subunit, suggesting that this unique subunit could mediate the solubility of the soluble rod PDE and the cone PDE in the intact photoreceptor. 相似文献
226.
Both the Entamoeba histolytica lectin, a virulence factor for the causative
agent of amebiasis, and the mammalian hepatic lectin bind to
N-acetylgalactosamine (GalNAc) and galactose (Gal) nonreducing termini on
oligosaccharides, with preference for GalNAc. Polyvalent GalNAc-
derivatized neoglycoproteins have >1000-fold enhanced binding affinity
for both lectins (Adler,P., Wood,S.J., Lee,Y.C., Lee,R.T., Petri,W.A.,Jr.
and Schnaar,R.L.,1995, J. Biol. Chem ., 270, 5164-5171). Substructural
specificity studies revealed that the 3-OH and 4-OH groups of GalNAc were
required for binding to both lectins, whereas only the E.histolytica lectin
required the 6-OH group. Whereas GalNAc binds with 4-fold lower affinity to
the E.histolytica lectin than to the mammalian hepatic lectin,
galactosamine and N-benzoyl galactosamine bind with higher affinity to the
E. histolytica lectin. Therefore, a synthetic scheme for converting
polyamine carriers to poly-N-acyl galactosamine derivatives (linked through
the galactosamine primary amino group) was developed to test whether such
ligands would bind the E.histolytica lectin with high specificity and high
affinity. Contrary to expectations, polyvalent derivatives including
GalN6lys5, GalN4desmosine, GalN4StarburstTMdendrimer, and
GalN8StarburstTMdendrimer demonstrated highly enhanced binding to the
mammalian hepatic lectin but little or no enhancement of binding to the
E.histolytica lectin. We propose that the mammalian hepatic lectin binds
with greatest affinity to GalNAc "miniclusters," which mimic branched
termini of N-linked oligosaccharides, whereas the E.histolytica lectin
binds most effectively to "maxiclusters," which may mimic more widely
spaced GalNAc residues on intestinal mucins.
相似文献
227.
Bioremediation Potential of Cr(VI)-Contaminated Soil Using Indigenous Microorganisms 总被引:1,自引:0,他引:1
Amendment of Cr(VI)-contaminated soil (approx. 200 mg/kg) with various treatments resulted in greater CO2 evolution and Cr(VI) reduction with organic amendments relative to controls receiving no organics, indicating bacterial reduction of Cr(VI) under anaerobic conditions. Isolation of Cr(VI)-reducing, indigenous bacteria, representative of the dominant soil population, further indicated Cr(VI) reduction by indigenous bacteria. Although desorption of Cr(VI) was evident with some treatments, its reduction was not affected. 相似文献
228.
229.
230.
High risk populations and HIV-1 infection in China 总被引:1,自引:0,他引:1
Tuo Fu ZHU- * Chun Hui WANG Peng LIN Na HE Departments of Laboratory Medicine Departments of Microbiology University of Washington School of Medicine Seattle WA USA Programs in Infectious Diseases Fred Hutchinson Cancer Research Center Seattle WA - USA Guangdong Center for Disease Control Prevention Guangzhou China School of Public Health Fudan University Shanghai China 《Cell research》2005,(Z1)
INTRODUCTION HIV has spread to all of China’s 31 provinces, autono- mous regions and municipalities, creating one of the fast- est-growing HIV/AIDS epidemics in the world [1,2]. The HIV/AIDS epidemic in China has gone through three phases: the Entry Phase (1985 -1988), the Spreading Phase (1989-1994) and the Expansion Phase (1995- present). The striking increase of HIV-1 infections over the past few years may herald entry into a new fourth phase that will include much larger nu… 相似文献