Rhee M J, Horrocks W D, Kosow D P
J Biol Chem. 1984 Jun 25;259(12):7404-8.
7F0 ---- 5D0 excitation spectroscopy of Eu(III) has shown that human Factor Xa has two high affinity lanthanide ion-binding sites. The deuterium isotope effect on the reciprocal lifetime (tau-1) of excited Eu(III) in human Factor Xa has indicated that 2 to 3 water molecules remain on Eu(III) after being complexed by Factor Xa, suggesting that 3-6 ligand atoms are provided by the protein, probably through two or three gamma-carboxyglutamic acids (GLA). F orster -type interlanthanide energy transfer has been utilized to measure the distance between the high affinity metal ion-binding sites of human Factor Xa using Tb(III) as an energy donor and Nd(III), Ho(III), or Er(III) as energy acceptors. Tau-1 values of Tb(III) in the presence of the acceptor ions Nd(III), Ho(III), and Er(III) were 1.90, 1.66, and 1.76 ms-1, respectively, which compared to 1.31 ms-1 in the presence of the nonacceptor ion Gd(III), yield energy transfer efficiencies of 0.29, 0.20, and 0.24, respectively. From these efficiencies and published critical distances (R0) ( Horrocks , W. DeW ., Jr., Rhee , M-J., Snyder, A. P., and Sudnick , D. R. (1980) J. Am. Chem. Soc. 102, 3650-3652), the distance between two high affinity sites is estimated to be 10.7 A. Based on these data, we propose that the two high affinity sites of human Factor Xa consist of two paired GLA residues; GLA-19, GLA-20 and GLA-25, GLA-26 together with one of the remaining single GLA residues for each site.
铕（III）的7F0 ---- 5D0激发光谱表明，人凝血因子Xa有两个高亲和力镧系离子结合位点。氘同位素对人凝血因子Xa中激发态铕（III）的倒数寿命（τ-1）的影响表明，铕（III）与凝血因子Xa络合后仍有2至3个水分子，这表明该蛋白质提供了3至6个配体原子，可能是通过两三个γ-羧基谷氨酸（GLA）。已利用弗斯特型镧系元素间能量转移，以铽（III）作为能量供体，钕（III）、钬（III）或铒（III）作为能量受体，来测量人凝血因子Xa高亲和力金属离子结合位点之间的距离。在存在受体离子钕（III）、钬（III）和铒（III）的情况下，铽（III）的τ-1值分别为1.90、1.66和1.76 ms-1，相比之下，在存在非受体离子钆（III）时为1.31 ms-1，相应的能量转移效率分别为0.29、0.20和0.24。根据这些效率和已发表的临界距离（R0）（霍罗克斯，W. 德W.，小，李，M-J.，斯奈德，A. P.，和苏德尼克，D. R.（1980）《美国化学会志》102，3650 - 3652），估计两个高亲和力位点之间的距离为10.7埃。基于这些数据，我们提出人凝血因子Xa的两个高亲和力位点由两对GLA残基组成；GLA - 19、GLA - 20和GLA - 25、GLA - 26，每个位点再加上其余单个GLA残基中的一个。
