Fullerton G D, Finnie M F, Hunter K E, Ord V A, Cameron I L
Department of Radiology, University of Texas HSCSA, San Antonio 78284.
Magn Reson Imaging. 1987;5(5):353-70. doi: 10.1016/0730-725x(87)90125-1.
The docking or polymerization of globular proteins is demonstrated to cause changes in proton NMR spin-lattice (T1) relaxation times. Studies on solutions of lysozyme, bovine serum albumin, actin, and tubulin are used to demonstrate that two mechanisms account for the observed changes in T1. Polymerization displaces the hydration water sheath surrounding globular proteins in solution that causes an increase in T1. Polymerization also slows the average tumbling rate of the proteins, which typically causes a contrary decrease in T1. The crystallization reaction of lysozyme in sodium chloride solution further demonstrates that the "effective" molecular weight can either decrease or increase T1 depending on how much the protein is slowed. The displacement of hydration water increases T1 because it speeds up the mean motional state of water in the solution. Macromolecular docking typically decreases T1 because it slows the mean motional state of the solute molecules. Cross-relaxation between the proteins and bound water provides the mechanism that allows macromolecular motion to influence the relaxation rate of the solvent. Fast chemical exchange between bound, structured, and bulk water accounts for monoexponential spin-lattice relaxation. Thus the spin-lattice relaxation rate of water in protein solutions is a complex reflection of the motional properties of all the molecules present containing proton magnetic dipoles. It is expected, as a result, that the characteristic relaxation times of tissues will reflect the influence of polymerization changes related to cellular activities.
球状蛋白质的对接或聚合被证明会导致质子核磁共振自旋晶格（T1）弛豫时间发生变化。对溶菌酶、牛血清白蛋白、肌动蛋白和微管蛋白溶液的研究表明，有两种机制可以解释观察到的T1变化。聚合作用会取代溶液中球状蛋白质周围的水化水鞘，从而导致T1增加。聚合作用还会减缓蛋白质的平均翻滚速率，这通常会导致T1出现相反的降低。溶菌酶在氯化钠溶液中的结晶反应进一步表明，“有效”分子量可能会根据蛋白质减缓的程度而使T1降低或增加。水化水的取代会增加T1，因为它加快了溶液中水的平均运动状态。大分子对接通常会降低T1，因为它减缓了溶质分子的平均运动状态。蛋白质与结合水之间的交叉弛豫提供了一种机制，使大分子运动能够影响溶剂的弛豫速率。结合水、结构化水和大量水之间的快速化学交换导致了单指数自旋晶格弛豫。因此，蛋白质溶液中水的自旋晶格弛豫速率是对所有含有质子磁偶极子的分子运动特性的复杂反映。因此，可以预期，组织的特征弛豫时间将反映与细胞活动相关的聚合变化的影响。
