Gutsze A, Bodurka J, Olechnowicz R, Buntkowsky G, Limbach H H
Department of Biophysics, Medical Academy of Bydgoszcz, Poland.
Z Naturforsch C J Biosci. 1995 May-Jun;50(5-6):410-8.
The dynamic properties of water molecules in the rabbit lens were studied by proton nuclear magnetic resonance line shape analysis, measurements of relaxation times as a function of temperature and calorimetric measurements. The experiments prove, as already suggested by other authors, that there are two types of water in the lens of rabbit eyes, namely bound unfreezable hydration water and bulk freezable water. Line shape analysis and relaxometry showed, that this two types of water exist in two different environments, which may be identified as the nucleus and the cortex of the lens. The line shape analysis showed furthermore that water molecules in the rabbit lens has a common spin lattice relaxation time (T1), but two different transverse relaxation times (T2A and T2B). The tentative model of fast water exchange on the T1 time scale and slow water exchange on the T2 time scale, was used to explain experimental proton relaxation data of the rabbit lens. An estimation for this exchange rate kex by comparing it to the relaxation times is given (T1(-1) << kex << T1(-1)). It has also been shown by a calorimetric measurements, that the lenses can be easily under-cooled to temperatures well below the freezing point of water. The achievable maximum undercooling temperature of the lens is a function of the cooling rate KC, therefore it has to be considered as an experimentally adjustable parameter which is not characteristic for the investigated sample. Thus it must be noted that any previous discussions about the specific value of the temperature of water crystallisation in biological systems need to be carefully reconsidered.
通过质子核磁共振线形状分析、弛豫时间随温度变化的测量以及量热测量，研究了兔晶状体中水分子的动态特性。正如其他作者已经指出的那样，实验证明兔眼晶状体中有两种类型的水，即结合的不可冻结的水化水和大量可冻结的水。线形状分析和弛豫测量表明，这两种类型的水存在于两种不同的环境中，可分别确定为晶状体的核和皮质。线形状分析还表明，兔晶状体中的水分子具有共同的自旋晶格弛豫时间（T1），但有两种不同的横向弛豫时间（T2A和T2B）。利用T1时间尺度上快速水交换和T2时间尺度上缓慢水交换的初步模型来解释兔晶状体的实验质子弛豫数据。通过将其与弛豫时间进行比较，给出了这种交换率kex的估计值（T1(-1) << kex << T1(-1)）。量热测量还表明，晶状体很容易被过冷到远低于水冰点的温度。晶状体可达到的最大过冷温度是冷却速率KC的函数，因此必须将其视为一个实验可调参数，而不是所研究样品的特征参数。因此必须注意，以前关于生物系统中水结晶温度具体值的任何讨论都需要仔细重新考虑。
