Koenig S H
Relaxometry Inc., Mahopac, New York 10541, USA.
Biophys J. 1995 Aug;69(2):593-603. doi: 10.1016/S0006-3495(95)79933-7.
Immobilized protein solute, approximately 20 wt %, alters the longitudinal and transverse nuclear magnetic relaxation rates 1/T1 and 1/T2 of solvent water protons in a manner that makes their values indistinguishable from those of a typical human tissue. There is now a quantitative theory at the molecular level (S.H. Koenig and R. D. Brown III (1993) Magn. Reson. Med. 30:685-695) that accounts for this, as a function of magnetic field strength, in terms of several distinguishable classes of water-binding sites at the protein-water interface at which significant relaxation and solute-solvent transfer of proton Zeeman energy occur. We review the arguments that these several classes of sites, characterized by widely disparate values of the resident lifetimes tau M of the bound waters, are associated with different numbers of hydrogen bonds that stabilize the particular protein-water complex. The sites that dominate relaxation-and produce contrast in magnetic resonance imaging (MRI), which derives from 1/T1 and 1/T2 of tissue water protons-have tau M approximately 10(-6)s. These, which involve four hydrogen bonds, occupy < or = 1% of the protein-water interface. Sites that involve three bonds, although more numerous, have < or = 20% smaller intrinsic effect on relaxation. The greater part of the "traditional" hydration monolayer, with even shorter-lived hydrogen-bonded waters, has little influence on solvent relaxation and is relatively unimportant in MRI. Finally, we argue, from the data, that most of the protein of tissue (a typical tissue is mostly protein) must be rotationally immobile (with Brownian rotational relaxation times slower than that of a 5 x 10(7) Da (very heavy) globular protein). We propose a functional basis for this immobilization ("cytoplasmic order"), and then indicate a way in which this order can break down ("cytoplasmic chaos") as a result of neoplastic transformation (cancer) and alter water-proton rates of pathological tissue and, hence, image contrast in MRI.
固定化的蛋白质溶质（约20 wt%）会改变溶剂水质子的纵向和横向核磁共振弛豫率1/T1和1/T2，使其值与典型人体组织的值难以区分。现在有一个分子水平的定量理论（S.H. 凯尼格和R.D. 布朗三世（1993年），《磁共振医学》30:685 - 695）可以解释这一现象，该理论根据磁场强度，从蛋白质 - 水界面上几类可区分的水结合位点出发，在这些位点上质子塞曼能量发生显著的弛豫和溶质 - 溶剂转移。我们回顾了这样的观点，即这些以结合水的驻留寿命tau M值差异很大为特征的几类位点，与稳定特定蛋白质 - 水复合物的不同数量的氢键相关。主导弛豫并在磁共振成像（MRI）中产生对比度的位点（MRI源自组织水质子的1/T1和1/T2），其tau M约为10^(-6)秒。这些位点涉及四个氢键，占蛋白质 - 水界面的比例≤1%。涉及三个氢键的位点虽然数量更多，但对弛豫的内在影响要小≤20%。“传统”水合单层中寿命更短的氢键结合水，对溶剂弛豫影响很小，在MRI中相对不重要。最后，我们根据数据认为，组织中的大部分蛋白质（典型组织大多是蛋白质）必定是旋转不动的（布朗旋转弛豫时间比5×10^7 Da（非常重）的球状蛋白质慢）。我们提出了这种固定化（“细胞质有序”）的功能基础，然后指出由于肿瘤转化（癌症）这种有序如何可能瓦解（“细胞质混乱”），并改变病理组织的水质子速率，进而改变MRI中的图像对比度。
