Ottolenghi P
Eur J Biochem. 1979 Aug 15;99(1):113-31. doi: 10.1111/j.1432-1033.1979.tb13238.x.
Enzymatically inactive, delipidated Na,K-ATPase from dogfish rectal glands was titrated with dioleoylphosphatidylcholine and with dioleoylphosphatidylethanolamine. The process of relipidation has the following characteristic properties. Enzymatic activities reappear independently of each other: first the phosphatase, then the ATPase. The properties of the phosphatase regenerated depend on the ratio of lipid/protein used; the ATPase seems to be independent of this ratio. The simplest model that is consistent with the above results and with the shapes of the titration curves, has the following requirements. Firstly, the enzyme is composed of two subunits that, as far as lipid binding is concerned, are identical and independent of each other. Secondly, lipid adds onto the enzyme as preformed clumps of 25 molecules of phosphatidylcholine or 18 molecules of phosphatidylethanolamine. Thirdly, each subunit binds two clumps of lipid, and binding shows positive cooperativity. Fourthly, when either subunit becomes saturated with lipid, the enzyme exhibits one form of phosphatase. Fifthly, when both subunits are saturated with lipid, the enzyme exhibits a second form of phosphatase and ATPase. The data and their analysis according to this model lead to the suggestion that Na,K-ATPase is a functional dimer, the interaction between subunits being influenced by the Na+ and K+ concentrations in the medium: K+ favouring the functional independence of the subunits and Na+ favouring their functional interaction.
用二油酰磷脂酰胆碱和二油酰磷脂酰乙醇胺对来自角鲨直肠腺的无酶活性、脱脂的钠钾 - ATP 酶进行滴定。再脂化过程具有以下特性。酶活性彼此独立地重新出现：首先是磷酸酶，然后是 ATP 酶。再生的磷酸酶的特性取决于所用脂质/蛋白质的比例；而 ATP 酶似乎与该比例无关。与上述结果及滴定曲线形状相符的最简单模型有以下要求。首先，该酶由两个亚基组成，就脂质结合而言，它们彼此相同且相互独立。其次，脂质以 25 个磷脂酰胆碱分子或 18 个磷脂酰乙醇胺分子预先形成的团簇形式添加到酶上。第三，每个亚基结合两团脂质，且结合表现出正协同性。第四，当任一亚基被脂质饱和时，酶表现出一种磷酸酶形式。第五，当两个亚基都被脂质饱和时，酶表现出第二种磷酸酶和 ATP 酶形式。根据该模型对数据及其分析表明，钠钾 - ATP 酶是一种功能性二聚体，亚基之间的相互作用受培养基中 Na⁺和 K⁺浓度的影响：K⁺有利于亚基的功能独立性，而 Na⁺有利于它们的功能相互作用。
