Lopina O D, Pindel E V, Boldyrev A A
Department of Biochemistry, School of Biology, Moscow State University, USSR.
FEBS Lett. 1990 Jun 18;266(1-2):75-7. doi: 10.1016/0014-5793(90)81510-u.
A conformational transition between E2 and E1 forms of Na, K-ATPase induced by different nucleotides has been studied under steady state conditions using the enzyme labelled with 5-iodoacetamidofluorescein. In the presence of K+ the plot of fluorescence as a function of [ATP], [ADP] or [CTP] (in a range of 5 microM-12 mM) is a biphasic one. A similar dependence for AMP, ITP, GTP and UTP demonstrates a hyperbolic behaviour. The data suggest that the shift in the equilibrium between E2 and E1 forms of Na,K-ATPase towards the E1 conformation is induced by ATP binding both with high and low affinity sites. Two structural features of ATP are apparently important for its interaction with more than one type of ATP binding sites or for providing for E2-E1 transition induced by this interaction: (i) beta-phosphate group in the terminal part of the molecule, (ii) unprotonated N1 and/or NH2-group in the 6th position of the purine base.
利用5-碘乙酰氨基荧光素标记的酶，在稳态条件下研究了不同核苷酸诱导的钠钾ATP酶E2和E1形式之间的构象转变。在钾离子存在的情况下，荧光强度与[ATP]、[ADP]或[CTP]（浓度范围为5微摩尔至12毫摩尔）的函数关系曲线呈双相。对于AMP、ITP、GTP和UTP，类似的依赖性表现为双曲线行为。数据表明，钠钾ATP酶E2和E1形式之间的平衡向E1构象的转变是由ATP与高亲和力和低亲和力位点结合诱导的。ATP的两个结构特征显然对其与多种类型的ATP结合位点相互作用或为这种相互作用诱导的E2-E1转变提供支持很重要：（i）分子末端部分的β-磷酸基团，（ii）嘌呤碱基第6位未质子化的N1和/或NH2基团。
