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461.
An experimentally-based modelling technique was applied to describequantitatively the uptake, translocation, storage, and assimilationof  相似文献   
462.
Time-resolved measurements of currents generated by Ca-ATPase from fragmented sarcoplasmic reticulum (SR) are described. SR vesicles spontaneously adsorb to a black lipid membrane acting as a capacitive electrode. Charge translocation by the enzyme is initiated by an ATP concentration jump performed by the light-induced conversion of an inactive precursor (caged ATP) to ATP with a time constant of 2.0 ms at pH 6.2 and 24 degrees C. The shape of the current signal is triphasic, an initial current flow into the vesicle lumen is followed by an outward current and a second slow inward current. The time course of the current signal can be described by five relaxation rate constants, lambda1 to lambda5 plus a fixed delay D approximately 1-3 ms. The electrical signal shows that 1) the reaction cycle of the Ca-ATPase contains two electrogenic steps; 2) positive charge is moved toward the luminal side in the first rapid step and toward the cytoplasmic side in the second slow step; 3) at least one electroneutral reaction precedes the electrogenic steps. Relaxation rate constant lambda3 reflects ATP binding, with lambda(3,max) approximately 100 s(-1). This step is electroneutral. Comparison with the kinetics of the reaction cycle shows that the first electrogenic step (inward current) occurs before the decay of E2P. Candidates are the formation of phosphoenzyme from E1ATP (lambda2 approximately 200 s[-1]) and the E1P --> E2P transition (D approximately 1 ms or lambda1 approximately 300 s[-1]). The second electrogenic transition (outward current) follows the formation of E2P (lambda4 approximately 3 s[-1]) and is tentatively assigned to H+ countertransport after the dissociation of Ca2+. Quenched flow experiments performed under the conditions of the electrical measurements 1) demonstrate competition by caged ATP for ATP-dependent phosphoenzyme formation and 2) yield a rate constant for phosphoenzyme formation of 200 s(-1). These results indicate that ATP and caged ATP compete for the substrate binding site, as suggested by the ATP dependence of lambda3 and favor correlation of lambda2 with phosphoenzyme formation.  相似文献   
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F Hartung  H Puchta 《Gene》2001,271(1):81-86
The Spo11 protein is an eukaryotic homologue of the topoisomerase 6 subunit A from archaebacteria. In yeast Spo11p has been found to bind covalently to double-strand breaks (DSBs) during meiosis. Single homologues of the SPO11 gene exist in various eukaryotes, except plants. Previously, we found in the Arabidopsis thaliana genome two ancient paralogs, AtSPO11-1 and 2. Here we report on the molecular characterization of a third one, AtSPO11-3. This puzzling finding might be explained by the fact that we detected additionally--for the first time outside of the archaebacterial kingdom--a homologue of the subunit B of topoisomerase 6, AtTOP6B. Both AtSPO11-3 and AtTOP6B are abundantly expressed in Arabidopsis and EST comparisons indicate the presence of both genes in various plant species. Via two hybrid studies we could demonstrate that full length AtTop6B is able to interact with AtSpo11-2 and 3 but not with AtSpo11-1. Our data suggest that plants possess in contrast to other eukaryotes an additional archaebacterial kind of topoisomerase.  相似文献   
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Rapidly accumulating evidence indicates that light reduces the human pineal's inhibitory effect on the gonads. Artificially extended daily photoperiods, by allowing increased production of gonadal steroids, have probably accentuated the secular growth trend and may be causing males, especially adolescents and young adults, to have an overready hormonal response to situations which elicit aggressive behavior.The author thanks George M. Vaughan, Harry J. Lynch, Mark D. Altschule, Edmund M. Dewan, Solomon H. Katz, George Adelman, John Ott, and Melvin J. Konner for much needed encouragement and edification. Thanks also to Heide Duda and Wesley Taoka (Countway Library, reference desk, Harvard Medical School) for gracious help on so many occasions.  相似文献   
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Wolfram Hartung 《Planta》1976,128(1):59-62
Summary One h and 3 h after point source application of [2-14C] ABA to the upper side of geotropically stimulated root tips of intact seedlings of Phaseolus coccineus L. a weak downward lateral transport of radioactivity was observed. A clear upward lateral translocation, however, occurred when ABA was applied to the lower side of the root tip. Thus a uniform distribution of radioactivity was established in horizontal roots regardless of the site of the application point, while in upright roots the distribution was asymmetric. Six h after ABA injection radioactivity was uniformly distributed in both the vertical and horizontal root tips.
Abkürzungen ABA Abscisinsäure - dpm disintegrations perminute - FG Frischgewicht - GA Gibberellinsäure  相似文献   
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