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Isolated human red blood cell membrane fragments (RBCMF) were found to take up Ca++ in the presence of ATP.1 This ATP-dependent Ca++ uptake by RBCMF appears to be the manifestation of an active Ca++ transport mechanism in the red cell membrane reported previously (Schatzmann, 1966; Lee and Shin, 1969). The influences of altering experimental conditions on Ca++-stimulated Mg++ ATPase (Ca++ ATPase) and Ca++ uptake of RBCMF were studied. It was found that pretreatment of RBCMF at 50°C abolished both Ca++ ATPase and Ca++ uptake. Pretreatment of RBCMF with phospholipases A and C decreased both Ca++ ATPase and Ca++ uptake, whereas pretreatment with phospholipase D did not significantly alter either Ca++ ATPase or Ca++ uptake. Both Ca++ ATPase and Ca++ uptake had ATP specificity, similar optimum pH's, and optimum incubation temperatures. From these results, it was concluded that Ca++ uptake is intimately linked to Ca++ ATPase.  相似文献   

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Polarographic investigation of binding of Cu++ and Cd++ by DNA   总被引:1,自引:0,他引:1  
D Bach  I R Miller 《Biopolymers》1967,5(2):161-172
The equilibrium binding constants of Cd++ and Cu++ to native and denatured calf thymus DNA were determined polarographically. The binding constants are an exponential function of the potential at the binding site and as such they vary with ionic strength and with the charge on the DNA molecule. The correlation between the fraction of sites occupied by heavy metal ions and between the thermal stability of DNA in solution is discussed.  相似文献   

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We have studied by X-ray diffraction fibres of complexes of polypurine-polypyrimidine with divalent cations. In the presence of Mg++, poly(dC) and poly(dG) form a very stable triple helix at neutral pH, based on G-G-C triplexes, whereas Zn++ prevents its formation, both at neutral and acidic pH. The poly(dC) . poly(dG) complex with Zn++ is of the B form, but its X-ray diffraction pattern shows an unusual intensity distribution. This is probably due to the fact that counterions occupy defined positions on the helix. The A form has not been observed. With poly[d(A-G)].poly [d(C-T)] a different triple helical structure is formed, both with Zn++ and Mg++. Direct, X-ray diffraction evidence for these triple helices is provided here for the first time.  相似文献   

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Summary Residual, i.e., (ouabain, bumetanide, and EGTA)-insensitive K+ and Na+ influxes as well as effluxes of human red blood cells are enhanced in isotonic solutions of low (Na-Cl+KCl) concentration using sucrose to maintain constant osmolarity. Various carrier models were tested to fit the experimental data of these fluxes simultaneously. The residual K+ and Na+ fluxes can be described on the basis of a carrier mechanism of competing substrates with modifier sites.  相似文献   

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Vanadate inhibits the Ca++-ATPase of sarcoplasmic reticulum from pig heart half maximally at about 10?5 M. Mg++ promotes this inhibition by vanadate whereas increasing Ca++-concentrations protect the enzyme against vanadate inhibition. Keeping the ratio Mg++ATP constant there was no influence of ATP on the vanadate inhibition at concentrations up to 5 × 10?3 M ATP. Whenever the ratio Mg++ATP was higher than 1:1 the inhibitory effect of vanadate on the Ca++-ATPase was increased.  相似文献   

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The active transport of Mg++ and Mn++ into the yeast cell   总被引:5,自引:6,他引:5  
Certain bivalent cations, particularly Mg++ and Mn++, can be absorbed by yeast cells, provided that glucose is available, and that phosphate is also absorbed. The cation absorption is stimulated by potassium in low concentrations, but inhibited by higher concentrations. From the time course studies, it is apparent that the absorption rather than the presence of phosphate and the potassium is the important factor. Competition studies with pairs of cations indicate that binding on the surface of the cell is not a prerequisite to absorption. The absorption mechanism if highly selective for Mg++ and Mn++, as compared to Ca++, Sr++, and UO2++, whereas the binding affinity is greatest for UO2++, with little discrimination between Mg++, Ca++, Mn++, and Sr++. In contrast to the surface-bound cations which are completely exchangeable, the absorbed cations are not exchangeable. It is concluded that Mg++ and Mn++ are actively transported into the cell by a mechanism involving a phosphate and a protein constituent.  相似文献   

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Mg++ like Ca++ induces a conformational change in the Ca++-binding component of troponin. However, this change is only 36 % of the change in fluorescence intensity and 80 % of the change in optical rotation induced by Ca++. The apparent binding constant of Mg++ to the Ca++-binding component is 5 × 103 M−1, much smaller than that of Ca++. Circular dichroism measurements show that these changes are simple helix-coil transitions. Unlike the Ca++-induced conformational change, the Mg++-induced change cannot be propagated to other muscle proteins, and therefore has no physiological meaning.  相似文献   

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The binding of Mg2+ and Mn2+ by DNA by a divalent cation specific electrode and by ultracentrifugation. Both techniques give similar results for the stoichiometry of the reaction. An oscillating densiemete allowed us to detect small changes of volume accompanying the binding. The reaction was also followed by circular dichroism measurements. Interpretation of the results is only possible if one assumes an electrostate site-binding of Mg2+ to phosphate group, and a chelation Mn2+ between the phosphate group and the N7 of the guanine. Physical modifications accompanying these two types of binding are discused and compared to the role of these cations in some biological systems involving DNA.  相似文献   

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