The Gd3+ complex of a fatty acid analogue of DOTP binds to multiple albumin sites with variable water relaxivities
The Gd3+ complex of a fatty acid analogue of DOTP binds to multiple albumin sites with variable water relaxivities
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DOI：
10.1021/ic0102900
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发表时间：
2001-12-17
影响因子：
4.6
通讯作者：
Sherry, AD
中科院分区：
文献类型：
--
作者：
Caravan, P;Greenfield, MT;Sherry, AD
20 MHz的水弛豫率（r（1））的钆（III）的配合物形成的两个脂肪酸类似物的1，4，7，10-四氮杂环十二烷-1，4，7，10-四（亚甲基膦酸酯）被证明在白蛋白的存在下，大大增加。Gd（C-8-DOTP）（5-）和Gd（C-11-DOTP）（5-）在水中的r（1）值与母体GdDOTP 5-（一种已知通过外层机制非常有效地弛豫水的q = 0络合物）的r（1）值相似。无论是脂肪酸类似物形成明显的聚集体或胶束在水中高达20 mM，但都显示出显着增加r（1）后，加入白蛋白。在非脱脂HSA存在下对Gd（C-11-DOTP）（5-）进行的进一步超滤研究表明，该复合物至少在5个高亲和力脂肪酸位点结合，逐步结合常数范围为1.27 x 10（5）至2.7 x 10（3）M-1。Gd（C-11-DOTP）（5-）在过量HSA存在下的20 MHz弛豫率在25 ℃时为23 mM（-1）s（-1）。NMR RD曲线显示出宽的最大值20-30 MHz，这与具有快速外层水交换的q = 0络合物的标准理论非常吻合。Gd（C-11-DOTP）（5-）在HSA最紧密位点结合的r（1b）在5 ℃时与40 mM（-1）s（-1）相似，这对于外层复合物来说是一个非常高的值。然而，Gd（C-11-DOTP）（5-）在HSA上较弱位点结合的r（1b）相当低，接近于自由络合物在水中的弛豫率。这表明结合在最高亲和力脂肪酸位点的复合物比结合在较弱亲和力脂肪酸位点的相同复合物的移动的少。这种结合超滤和弛豫研究表明，一个单一的r（1b）值的Gd 3+复合物结合在几个蛋白质位点的共同假设是不是一个有效的近似。
The 20 MHz water relaxivity (r(1)) of gadolinium(III) complexes formed with two fatty acid analogues of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylene phosphonate) were shown to increase substantially in the presence of albumin. The r(1) values of Gd(C-8-DOTP)(5-) and Gd(C-11-DOTP)(5-) in water were similar to that of the parent GdDOTP5-, a q = 0 complex known to relax water very efficiently via an outer-sphere mechanism. Neither fatty acid analogue formed apparent aggregates or micelles in water up to 20 mM, but both showed dramatic increases in r(1) upon addition of albumin. Further ultrafiltration studies of Gd(C-11-DOTP)(5-) in the presence of non-defatted HSA showed that the complex binds at a minimum of five high-affinity fatty acid sites with stepwise binding constants ranging from 1.27 x 10(5) to 2.7 x 10(3) M-1. The 20 MHz relaxivity of Gd(C-11-DOTP)(5-) in the presence of excess HSA was 23 mM(-1) s(-1) at 25 degreesC. The NMRD curve showed a broad maximum 20-30 MHz which fitted well to standard theory for a q = 0 complex with rapid outer-sphere water exchange. The r(1b) of Gd(C-11-DOTP)(5-) bound at the tightest site on HSA was similar to 40 mM(-1) s(-1) at 5 degreesC, an extraordinarily high value for an outer-sphere complex. However, the r(1b) of Gd(C-11-DOTP)(5-) bound at the weaker sites on HSA was considerably lower, approaching the relaxivity of the free complex in water. This suggests that the complex bound in the highest affinity fatty acid site is less mobile than the same complex bound at the weaker affinity fatty acid sites. This combined ultrafiltration and relaxivity study demonstrates that the common assumption of a single r(1b) value for a Gd3+ complex bound at several protein sites is not a valid approximation.