Zhong J H, Gore J C, Armitage I M
Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Magn Reson Med. 1989 Sep;11(3):295-308. doi: 10.1002/mrm.1910110304.
Transverse relaxation times T2 of water protons were measured in 5% protein solutions and soaked rat liver in different static magnetic fields (0.15 to 11 T). Protein molecular weight varied between 1.4 and 480 kDa in solutions of varying degrees of deuteration. The data obtained are analyzed in terms of a model system consisting of three phases of different relaxation characteristics: protein protons, hydration layer water protons, and bulk water protons. The contributions to relaxation due to hydrodynamic effects on water protons, cross relaxation between the hydration layer water protons and the protein protons, and chemical exchange between the hydration layer water protons and the bulk water protons are separately estimated. The experimental results indicate that the "hydrodynamic interactions" are about the same magnitude in rat liver and all the proteins studied, but the contribution of the cross relaxation differs by several orders in different protein systems. Fast chemical exchange between the hydration layer water and the bulk water causes considerable shortening of T2 at high magnetic fields for all the protein solutions and rat tissue studied. Selected samples were studied at different temperatures (213-318 K) and with different intervals in the CPMG sequence. The rates of chemical exchange and fractional populations of different phases are determined, and the results obtained provide support for the model in which fast exchange among the different water phases is an important feature of the overall relaxation behavior.
在不同静磁场（0.15至11 T）中，对5%蛋白质溶液和浸泡的大鼠肝脏中的水质子横向弛豫时间T2进行了测量。在不同氘化程度的溶液中，蛋白质分子量在1.4至480 kDa之间变化。根据由具有不同弛豫特性的三个相组成的模型系统对获得的数据进行分析：蛋白质质子、水化层水质子和体相水质子。分别估算了流体动力学对水质子的影响、水化层水质子与蛋白质质子之间的交叉弛豫以及水化层水质子与体相水质子之间的化学交换对弛豫的贡献。实验结果表明，“流体动力学相互作用”在大鼠肝脏和所有研究的蛋白质中大小大致相同，但交叉弛豫的贡献在不同蛋白质系统中相差几个数量级。对于所有研究的蛋白质溶液和大鼠组织，水化层水与体相水之间的快速化学交换在高磁场下会导致T2显著缩短。在不同温度（213 - 318 K）下，使用CPMG序列中的不同间隔对选定样本进行了研究。确定了化学交换速率和不同相的分数种群，所得结果为不同水相之间的快速交换是整体弛豫行为的一个重要特征这一模型提供了支持。
