Luisi B F, Nagai K
Nature. 1986;320(6062):555-6. doi: 10.1038/320555a0.
The expression of beta-globin in Escherichia coli has enabled us to study the functional role of individual amino-acid residues in haemoglobin (Hb) by site-directed mutagenesis. In contrast to mammalian Hbs, some teleost fish haemoglobins show a drastic lowering of oxygen affinity and cooperativity at low pH, a phenomenon known as the Root effect. We have produced the two mutant haemoglobins Hb Nymphéas [Cys(F9)93 beta----Ser] and Hb Daphne [His(H21)143 beta----Arg, Cys(F9)93 beta----Ser] to investigate this allosteric property. Although these substitutions were thought to be responsible for the Root effect, Hb Nymphéas and Hb Daphne show an increased oxygen affinity and a reduced effect of pH on oxygen affinity. Our X-ray crystallographic studies show that the hydroxyl group of Ser 93 beta forms a hydrogen bond with Asp 94 beta which is in equilibrium with the salt bridge between Asp 94 beta and His 146 beta. The oxygen-binding properties of Hbs Nymphéas and Daphne are accounted for by the partial disruption of the salt bridge.
β-珠蛋白在大肠杆菌中的表达使我们能够通过定点诱变研究血红蛋白（Hb）中单个氨基酸残基的功能作用。与哺乳动物的血红蛋白不同，一些硬骨鱼血红蛋白在低pH值下表现出氧亲和力和协同性的急剧降低，这种现象被称为鲁特效应。我们制备了两种突变血红蛋白Hb Nymphéas [Cys(F9)93β→Ser] 和Hb Daphne [His(H21)143β→Arg, Cys(F9)93β→Ser] 来研究这种别构性质。尽管这些取代被认为是鲁特效应的原因，但Hb Nymphéas和Hb Daphne表现出氧亲和力增加以及pH对氧亲和力的影响降低。我们的X射线晶体学研究表明，Ser 93β的羟基与Asp 94β形成氢键，该氢键与Asp 94β和His 146β之间的盐桥处于平衡状态。Hb Nymphéas和Daphne的氧结合特性是由盐桥的部分破坏所导致的。
