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61.
R Rothrock S T Perry K R Isham K L Lee F T Kenney 《Biochemical and biophysical research communications》1983,113(2):645-649
Rat fetuses of 20 days gestational age were treated in utero with the inhibitor of DNA methylation, 5-azacytidine. The liver enzyme tyrosine aminotransferase, normally expressed at very low levels until several hours after birth, was increased by the drug in the fetal livers after a lag period of about 9 hours, reaching a level 70-fold above control levels 18 hours after treatment. The high levels attained after 5-azacytidine treatment are comparable to those of glucocorticoid-treated adult livers, and were not further increased by administration of hydrocortisone to dams carrying treated fetuses. Cytidine and two other analogs, cytosine arabinoside and 6-azacytidine, were essentially without effect. 相似文献
62.
2,3-Butanedione inactivates the pure form of UDP-glucuronyltransferase used in these experiments (GT2P) (EC 2.4.1.17) purified from pig liver microsomes. The kinetics of the reaction indicates that 2,3-butanedione reacts with two amino acids that affect activity. A rapid, partial inactivation is followed by a slower rate of inactivation that leads eventually to completely inactive enzyme. UDP-glucuronic acid and glucuronic acid, as compared with UDP, are effective as protectors against the slow, secondary phase of inactivation; no ligand tested protected against the rapid phase of inactivation. The lipid environment of GT2P was a determinant of the pseudo-first order rate constant for the slow phase of inactivation, but did not affect the rate of the rapid phase of inactivation. The data suggest that GT2P contains an active site arginine that interacts with the -COO- at C-6 of the glucuronic acid moiety of UDP-glucuronic acid. 相似文献
63.
Apparent sucrose uptake. ATPase activity and membrane fluidity changes were studied during the development and senescence of carnation flowers ( Dianthus caryophyllus L., cv. Cerise Royallette). Typical changes associated with senescence of a cut flower, such as respiration, ethylene production and fresh weight, were measured. Concomitant with a rise in respiration and ethylene production and a decline in fresh weight, a sharp decrease in apparent sucrose uptake was observed. Sucrose uptake was pH dependent (pH optimum, 5.5) and influenced by membrane integrity. Apparently, the activity of ATPase is related to sucrose uptake, because similar changes occurred during flower development. In addition, the activity of ATPase was well correlated with membrane fluidity.
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed. 相似文献
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed. 相似文献
64.
Development and differentiation of the brain ventricular system in tadpoles of Xenopus laeris (Daudin) (Amphibia, Anura) 总被引:1,自引:0,他引:1
A Lametschwandtner A Laminger H Adam 《Zeitschrift für mikroskopisch-anatomische Forschung》1983,97(2):265-278
The development and the differentiation of the ventricular system of the brain of tadpoles of the South African Clawed Toad, Xenopus laevis (Daudin), is studied by light microscopy (stages 45 to 66) and scanning and transmission electron microscopy (stages 50 to 66). Special interest is paid to the ependymal structures of the foramen of Monroe, the ventricles of the diencephalon, the mesencephalon, and the rhombencephalon, and to the ependymal of the central canal and the choroid plexus of the third and fourth ventricle. At early developmental stages the lower two thirds of the ventricles are dominated by blebs, cytoplasmatic protrusions of the ependymal cells. During the development they become reduced and replaced by cilia. The number of cilia and microvilli increases strongly towards the end of the metamorphosis. The surface structures demonstrated by scanning electron microscopy are discussed in respect to morphology and physiology. 相似文献
65.
Donald Spencer Peter M. Chandler Thomas J. V. Higgins Adam S. Inglis Michael Rubira 《Plant molecular biology》1983,2(5):259-267
Serological studies and comparison of N-terminal amino acid sequences with the amino acid sequence deduced from a cDNA clone have been used to establish the sequence relationships between the subunits of the pea seed storage protein, vicilin. Subunits smaller than Mr~50 000 (i.e., Mr 34 000, 30 000, 25 000, 18 000, 14 000, 13 000 and 12 000) show extensive homology with molecules within Mr~50 000 group. Both the sequencing and serological data confirm earlier evidence from studies on vicilin synthesisin vivo andin vitro which indicated that the vicilin subunits smaller than Mr~50 000 arose by endoproteolytic cleavage of parent molecules within the Mr~50 000 group. Cleavage in different Mr 50 000 parent molecules containing either one or both of two susceptible processing sites accounts for the formation of all the vicilin subunits smaller than Mr~50 000, with the possible exception of the Mr34 000 polypeptide. The position of these sites in the putative parents were defined by reference to a complete amino acid sequence deduced from the sequence of DNA complementary to mRNA for one member of the Mr~50 000 group. 相似文献
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70.
Nuclear protein import in permeabilized mammalian cells requires soluble cytoplasmic factors 总被引:94,自引:41,他引:53 下载免费PDF全文
We have developed an in vitro system involving digitonin-permeabilized vertebrate cells to study biochemical events in the transport of macromolecules across the nuclear envelope. While treatment of cultured cells with digitonin permeabilizes the plasma membranes to macromolecules, the nuclear envelopes remain structurally intact and nuclei retain the ability to transport and accumulate proteins containing the SV40 large T antigen nuclear location sequence. Transport requires addition of exogenous cytosol to permeabilized cells, indicating the soluble cytoplasmic factor(s) required for nuclear import are released during digitonin treatment. In this reconstituted import system, a protein containing a nuclear location signal is rapidly accumulated in nuclei, where it reaches a 30-fold concentration compared to the surrounding medium within 30 min. Nuclear import is specific for a functional nuclear location sequence, requires ATP and cytosol, and is temperature dependent. Furthermore, accumulation of the transport substrate within nuclei is completely inhibited by wheat germ agglutinin, which binds to nuclear pore complexes and inhibits transport in vivo. Together, these results indicate that the permeabilized cell system reproduces authentic nuclear protein import. In a preliminary biochemical dissection of the system, we observe that the sulfhydryl alkylating reagent N-ethylmaleimide inactivates both cytosolic factor(s) and also component(s) in the insoluble permeabilized cell fraction required for nuclear protein import. Because this permeabilized cell model is simple, efficient, and works effectively with cells and cytosol fractions prepared from a variety of different vertebrate sources, it will prove powerful for investigating the biochemical pathway of nuclear transport. 相似文献