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961.
Isoleucine and Valine Metabolism in Escherichia coli XVIII. Induction of Acetohydroxy Acid Isomeroreductase 总被引:7,自引:7,他引:0
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The regulation by substrate induction of the acetohydroxy acid isomeroreductase was studied in Escherichia coli. Induction was inhibited by chloramphenicol and rifampin. The addition of rifampin resulted in a decay of the capacity to form isomeroreductase. This was attributed to the breakdown of the isomeroreductase messenger, which had a half-life of about 45 sec at 37 C. Induction of isomeroreductase was enhanced by including glucose in the medium. This effect was shown to be due in part to the lowering of the pH of the medium, which presumably made inducer entry more rapid. 相似文献
962.
963.
Abstract— 2-Hydroxy-, 2-chloro-, 2- and Cmethyl-GABA are linear competitive inhibitors of GABA uptake in rat brain slices. These analogues are thus potential substrates for the GABA transport system and possible'false transmitters'. 2-Hydroxy-GABA is the most potent inhibitor of GABA uptake yet described. No specific inhibitor of GABA uptake was revealed amongst the drugs tested. 相似文献
964.
965.
Measurement of profiles of potassium activity and electrical potential in the intact root 总被引:3,自引:0,他引:3
D. J. F. Bowling 《Planta》1972,108(2):147-151
Summary Profiles of potassium activity and electrical potential in the vacuoles of cells across the intact root of Helianthus annuus have been measured. No gradient in either potassium activity or potential difference was detected from epidermis to pericycle. The trans-root electrical potential was found to be made up of two components, a large P.D. between the outside solution and the outer cells and a small P.D. at the pericycle-xylem interface. The results indicated that all the living cells of the root have the same capacity to actively accumulate potassium. 相似文献
966.
AS it is not widely appreciated that diffusion within complex media can be strikingly and often qualitatively different from that in simple liquids such as water, there is confusion concerning transport processes across biological membranes1,2. We would like to draw attention to some fundamental differences between the diffusion process in simple liquids and that in more complex media-non-porous networks of hydrophobic polymers and biological membranes. 相似文献
967.
968.
969.
With the help of a suction manometric device, the relation between the deformation of Xenonus laevis embryo at the gastrula and neurula stages and the value of the applied force has been studied. Stiffness modules of embryonic
tissues were in the order of several dozens of Pascal and they were inversely proportional during deformation from 40 to 20%.
At the gastrula stage, a uniform or an increasing rate of expansion of the embryo body in the suction capillary with the diameter
of approximately half that of the embryo was observed for 30 min after the action of the suction forces. The length of the
stretched portion of the embryo correlates with the value of its deformation at the first minute. As a result of the expansion,
the total body surface area of the deformed embryo increases more than twice compared to intact embryos. After expelling the
embryo from the capillary, its surface reduced and the deformation became smoothened within 5 min, which indicates the existence
of tensional force in the expanded embryo. These data confirm that, at the embryo gastrula stage, external mechanical forces
do not only passively deform the embryo but also initiate the active expansion of the embryo which takes place at zero external
force and overcomes the tensional resistance of tissues. The mechanism of active expansion and its link with the processes
of normal morphogenesis are discussed. 相似文献
970.