Avaeva S M, Rodina E V, Kurilova S A, Nazarova T I, Vorobyeva N N, Harutyunyan E H
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation.
FEBS Lett. 1995 Dec 11;377(1):44-6. doi: 10.1016/0014-5793(95)01310-5.
Further refinement of X-ray data on Escherichia coli inorganic pyrophosphatase [Oganessyan et al. (1994) FEBS Lett. 348, 301-304] to 2.2 A reveals a system of noncovalent interactions involving Tyr55 and Tyr141 in the active site. The pKa for one of the eight Tyr residues in wild-type pyrophosphatase is as low as 9.1 and further decreases to 8.1 upon Mg2+ binding, generating characteristic changes in the absorption spectrum. These effects are lost in a Y55F but not in a Y141F variant. It is suggested that the lower-affinity site for Mg2+ in the enzyme is formed by Tyr55 and Asp70, which are in close proximity in the apo-enzyme structure.
大肠杆菌无机焦磷酸酶X射线数据[奥加涅相等人（1994年），《欧洲生物化学学会联合会快报》348卷，301 - 304页]进一步精修至2.2埃，揭示了一个涉及活性位点中Tyr55和Tyr141的非共价相互作用体系。野生型焦磷酸酶八个Tyr残基之一的pKa低至9.1，在结合Mg2+后进一步降至8.1，导致吸收光谱发生特征性变化。这些效应在Y55F变体中消失，但在Y141F变体中未消失。有人提出，酶中Mg2+的低亲和力位点由Tyr55和Asp70形成，它们在脱辅基酶结构中彼此靠近。
