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31.
Metabolism of
d-Glycero-d-Manno-Heptitol,
Volemitol, in Polyanthus. Discovery of a Novel Ketose
Reductase 下载免费PDF全文
Volemitol
(d-glycero-d-manno-heptitol,
α-sedoheptitol) is an unusual seven-carbon sugar alcohol that
fulfills several important physiological functions in certain species
of the genus Primula. Using the horticultural hybrid
polyanthus (Primula × polyantha) as
our model plant, we found that volemitol is the major nonstructural
carbohydrate in leaves of all stages of development, with
concentrations of up to 50 mg/g fresh weight in source leaves (about
25% of the dry weight), followed by sedoheptulose
(d-altro-2-heptulose, 36 mg/g fresh weight),
and sucrose (4 mg/g fresh weight). Volemitol was shown by the
ethylenediaminetetraacetate-exudation technique to be a prominent
phloem-mobile carbohydrate. It accounted for about 24% (mol/mol) of
the phloem sap carbohydrates, surpassed only by sucrose (63%).
Preliminary 14CO2 pulse-chase radiolabeling
experiments showed that volemitol was a major photosynthetic product,
preceded by the structurally related ketose sedoheptulose. Finally, we
present evidence for a novel NADPH-dependent ketose reductase,
tentatively called sedoheptulose reductase, in volemitol-containing
Primula species, and propose it as responsible for the
biosynthesis of volemitol in planta. Using enzyme extracts from
polyanthus leaves, we determined that sedoheptulose reductase has a pH
optimum between 7.0 and 8.0, a very high substrate specificity, and
displays saturable concentration dependence for both sedoheptulose
(apparent Km = 21 mm) and NADPH
(apparent Km = 0.4 mm). Our
results suggest that volemitol is important in certain
Primula species as a photosynthetic product, phloem
translocate, and storage carbohydrate.Alditols (sugar alcohols or acyclic polyols) may be chemically
described as reduction products of aldose or ketose sugars. The most
prevalent plant alditols are the hexitols sorbitol, mannitol, and
galactitol. However, as many as 17 different alditols occur naturally
in higher plants (for review, see Bieleski, 1982; Lewis, 1984; Loescher
and Everard, 1996). The lesser-known alditols are often restricted in
their occurrence but still fulfill important functions in those plants
where they do occur. Volemitol (Fig. (Fig.1)
1)
is a good example of a less common but important alditol. This
seven-carbon sugar alcohol seems to be confined to certain sections of
the genus Primula, so much so that it has been suggested as
a useful chemotaxonomical marker (Kremer, 1978). Very little is known
about the physiology and metabolism of volemitol in primulas, except
that it was an early photosynthetic product in cowslip (Primula
veris) and oxslip (Primula elatior) (Kremer, 1978).
Figure 1Fischer projections of volemitol and its four
structurally related seven-carbon sugars. Nomenclature follows that of
Collins (1987); trivial names are underlined.The physiological roles of alditols are manifold and largely resemble
those of disaccharides and oligosaccharides. They include
photosynthetic assimilation, translocation and storage of carbon, and
reducing power, as well as protection against different types of
stresses (for review, see Bieleski, 1982; Lewis, 1984; Loescher and
Everard, 1996; Stoop et al., 1996). The biosynthetic pathways of the
hexitols sorbitol (glucitol), mannitol, galactitol (dulcitol), and the
pentitol ribitol have been established in higher plants. They generally
use NADPH as a hydrogen donor and aldose phosphate as a hydrogen
acceptor, in concert with the corresponding phosphatases. One exception
might be galactitol, which was suggested to be formed directly from
unphosphorylated Gal (and NADPH) (Negm, 1986). Although all foliar
alditols are thought to be phloem-mobile (Lewis, 1984), this has only
been demonstrated for sorbitol, mannitol, and galactitol (Zimmermann
and Ziegler, 1975; Davis and Loescher, 1990; Moing et al., 1992; Flora
and Madore, 1993).To expand our knowledge of alditol metabolism in higher plants beyond
that of hexitols, we studied the carbohydrate metabolism of polyanthus
(Primula × polyantha). This popular
horticultural hybrid of primrose (Primula
vulgaris), oxlip, and cowslip (Mabberley, 1997) was
chosen because preliminary experiments showed that its volemitol
content is very high, similar to that of the wild-type species, and
because it may be easily grown both outdoors and indoors.We give a general overview on volemitol metabolism in polyanthus with
special emphasis on the role of volemitol in plant development and
phloem transport. We also report on a novel enzyme, a NADPH-dependent
ketose reductase, which forms volemitol by the reduction
of sedoheptulose. 相似文献
32.
33.
Conversion of bacteriophage fd into an efficient single-stranded DNA vector system 总被引:34,自引:0,他引:34
Richard Herrmann Kristina Neugebauer Elsbeth Pirkl Hanswalter Zentgraf Heinz Schaller 《Molecular & general genetics : MGG》1980,177(2):231-242
Summary Single-stranded DNA vectors were constructed in vitro by insertion of various DNA fragments into the Intergenic Region of the single-stranded DNA phage fd. These inserts introduce into the phage genome unique cleavage sites for restriction nucleases which are suited for sticky joining in cloning experiments. Since these sites are usually located within genes coding for antibiotic resistance, inactivation of a resistance gene by insertion can be used as a marker for the successful cloning of a DNA fragment. Resistance genes also allow to select for recombinant DNA phages and to minimize the loss of DNA inserts which otherwise becomes significant above an insert size of about one kb. Cloning of several DNA fragments is described and strand separation of double-stranded DNA fragments by means of cloning into fd DNA is given as an example for application of single-stranded DNA vectors.Abbreviations Ap
ampicillin
- Cm
chloramphenicol
- Km
kanamycin
- Sm
streptomycin
- kb, kbp
a unit length equivalent to 1000 bases, respectively 1000 base pairs
- wt
wild type 相似文献
34.
35.
36.
37.
38.
DNA synthesis, as measured by incorporation of [(3)H]TTP, was inhibited in Swiss mouse 3T3 cells treated with interferon and subsequently permeabilized with lysolecithin. The degree of inhibition observed was similar in intact or permeabilized cells. The interferon-induced antiviral state was retained in permeabilized cells. 相似文献
39.
Leyla Knittweis Wiebke Elsbeth Kraemer Janne Timm Marc Kochzius 《Conservation Genetics》2009,10(1):241-249
The fungiid Heliofungia actiniformis is one of the most popular scleractinian coral species in the growing live aquarium trade, with the majority of specimens
originating in Indonesia. Details on population connectivity may potentially provide important information with regards to
harvest management efforts. Genetic structure was examined, using ribosomal ITS1, 5.8S and partial ITS2 sequences on a small
scale among populations in the Spermonde Archipelago, South Sulawesi (up to 65 km distance, Φst = 0.09), and on a large scale throughout the Indo-Malay Archipelago (up to 2,900 km distance, Φst = 0.26). Significant genetic structuring was found at both scales. Within the Spermonde Archipelago isolation by distance
as well as local oceanographic features shaped patterns of genetic connectivity. On the large scale, the data revealed genetically
distinct populations in Tomini Bay, New Guinea and the Thousand Islands near Jakarta, and a lack of genetic differentiation
among populations lying close to or directly in the path of the Indonesian throughflow: from the central Visayas to the Flores
Sea (Φct = 0.32). Whilst the influence of both historical and present day processes on genetic structuring of H. actiniformis populations was revealed, large scale results further emphasised the importance of oceanographic dynamics on larval dispersal
patterns in this species. Potential for larval input from surrounding populations, and the increased vulnerability of upstream
as well as isolated populations should be taken into consideration when setting future harvest quotas. 相似文献
40.