The effect of pH, of ATP and of modification with pyridoxal 5-phosphate on the conformational transition between the Na+-form and the K+-form of the (Na+ +K+)-ATPase.
The effect of pH, of ATP and of modification with pyridoxal 5-phosphate on the conformational transition between the Na+-form and the K+-form of the (Na+ +K+)-ATPase.
复制标题
pH、ATP 和 5-磷酸吡哆醛修饰对 (Na K )-ATP 酶 Na 型和 K 型之间构象转变的影响。
DOI：
10.1016/0005-2736(82)90348-0
复制
发表时间：
1982
期刊：
影响因子：
--
通讯作者：
JENS CHR. Skou
中科院分区：
文献类型：
--
作者：
JENS CHR. Skou
pH值的增加会降低Na+浓度（Na++ K+= 150 mM），这是在非饱和浓度的ATP下（Na++ K+）-ATP酶的半最大激活所必需的，正如在给定pH下ATP浓度的增加一样。它还降低了在平衡条件下（Na++ K+= 150 mM）从K+-形式转化为Na+-形式所必需的Na+浓度。pH值的增加增加了系统从K+-形式到Na+-形式的转化速率，并降低了逆反应的速率。pH对构象的影响表明K+-型是质子化的形式，Na+-型是去质子化的形式。ATP浓度不饱和时pH值增加的效应与给定pH值下ATP浓度增加的效应之间的相似性表明，ATP通过降低系统的pK值，即通过释放质子，即玻尔效应，对从K+-到Na+-形式的转化产生影响。通过与NaBH 4终止的吡哆醛5-磷酸反应修饰的酶在给定的pH下表现得好像它是未修饰的酶，但在更高的pH下。在ATP存在下，Na+不存在和与ATP存在下，K+与ATP存在下，而不是在K+单独存在下，在吡哆醛5-磷酸修饰后，可以看到“pH效应”。改性也有一个“pH值效应”的转化率从K+-形式的Na+-形式和逆反应。存在至少两个不同的吡哆醛5-磷酸反应性基团（氨基），一个可以被ATP保护并且对于活性是重要的，另一个不被ATP保护并且对于构象的pH效应是重要的。氨基的质子化-去质子化对构象的影响被解释为氨基参与多肽链之间和内部的盐桥形成，血红蛋白样的情况。质子化的K+-形式则是具有高K+、低Na+亲和力的紧张T-结构，而去质子化的Na+-形式是具有高Na+、低K+亲和力的松弛R-结构。ATP通过降低pK值促进去质子化。在平衡和稳态条件下，寡霉素对Na ~+的K ~（0.5）有“pH效应”，但对K ~+-型向Na ~+-型转化的速率没有影响，但明显降低了逆反应的速率，表明寡霉素不与K ~+-型反应，而与Na ~+-型反应，阻止了质子化，从E1到E2的转换
An increase in pH decreases the Na+ concentration (Na++ K+= 150 mM) necessary for half-maximum activation of the (Na++ K+)-ATPase at non-saturating concentrations of ATP just as an increase in the concentration of ATP at a given pH. It also decreases the concentration of Na+ necessary for transformation from the K+-form to the Na+-form at equilibrium conditions (Na++ K+= 150 mM). An increase in pH increases the rate of the transformation from the K+-form to the Na+-form of the system and decreases the rate of the reverse reaction. The pH effect on the conformation suggests that the K+-form is a protonated form and the Na+-form a deprotonated one. The similarity between the effect of an increase in pH with non-saturating concentrations of ATP and that of an increase in ATP at a given pH suggests that ATP exerts its effect on the transformation from the K+-to the Na+-form by a decrease in p K values of the system, ie, by releasing protons, a Bohr effect. Enzyme modified by reaction with pyridoxal 5-phosphate terminated by NaBH 4 behaves at a given pH as if it were non-modified enzyme but at a higher pH. The ‘pH effect’is seen after modification by pyridoxal 5-phosphate in the presence of ATP, of Na+ without and with ATP, of K+ with ATP but not in the presence of K+ alone. The modification has also a ‘pH effect’on the rate of the transformation from the K+-form to the Na+-form and on the reverse reaction. There are at least two different pyridoxal 5-phosphate-reactive groups (amino groups), one which can be protected by ATP and which is of importance for activity and another which is not protected by ATP and which is of importance for the pH effect on the conformation. The effect of a protonation-deprotonation of amino groups on the conformation is explained by an involvement of the amino groups in salt bridge formation inbetween and inside the polypeptide chains, a hemoglobin-like situation. The protonated K+-form is then a tense T-structure with a high K+, low Na+ affinity and the deprotonated Na+-form a relaxed, R-structure with high Na+, low K+ affinity. ATP facilitates deprotonation by decreasing p K values. Oligomycin has ‘pH effect’on the K 0.5 for Na+ under equilibrium and steady-state conditions, but oligomycin has no effect on the rate of the transformation from the K+-form to the Na+-form, but gives a pronounced decrease of the rate of the reverse reaction, indicating that oligomycin does not react with the K+-form but with the Na+-form of the system and prevents the protonation, the E 1 to E 2 transformation.