A probability distribution of rate constants contained within an exponential-like saturation recovery (SR) electron paramagnetic resonance signal can be constructed using stretched exponential function fitting parameters. Previously (Stein et al. Appl. Magn. Reson. 2019.), application of this method was limited to the case where only one relaxation process, namely spin–lattice relaxations due to the rotational diffusion of the spin labels in the intact eye-lens membranes, contributed to an exponential-like SR signal. These conditions were achieved for thoroughly deoxygenated samples. Here, the case is described where the second relaxation process, namely Heisenberg exchange between the spin label and molecular oxygen that occurs during bimolecular collisions, contributes to the decay of SR signals. We have further developed the theory for application of stretched exponential function to analyze SR signals involving these two processes. This new approach allows separation of stretched exponential parameters, namely characteristic stretched rates and heterogeneity parameters for both processes. Knowing these parameters allowed us to separately construct the probability distributions of spin–lattice relaxation rates determined by the rotational diffusion of spin labels and the distribution of relaxations induced strictly by collisions with molecular oxygen. The later distribution is determined by the distribution of oxygen diffusion concentration products within the membrane, which forms a sensitive new way to describe membrane fluidity and heterogeneity. This method was validated in silico and by fitting SR signals from spin-labeled intact nuclear fiber cell plasma membranes extracted from porcine eye lenses equilibrated with different fractions of air.

中文翻译：

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饱和恢复 EPR 法测定眼晶状体纤维细胞质膜中的氧传输参数


包含在类指数饱和恢复（SR）电子顺磁共振信号内的速率常数的概率分布可以使用拉伸指数函数拟合参数来构建。此前（Stein et al. Appl. Magn. Reson. 2019），这种方法的应用仅限于只有一个弛豫过程的情况，即由于完整眼中自旋标签的旋转扩散而导致的自旋晶格弛豫。晶状体膜，产生了指数式的 SR 信号。彻底脱氧的样品达到了这些条件。在这里，描述了第二弛豫过程（即双分子碰撞期间发生的自旋标签和分子氧之间的海森堡交换）导致 SR 信号衰减的情况。我们进一步发展了应用拉伸指数函数来分析涉及这两个过程的 SR 信号的理论。这种新方法允许分离拉伸指数参数，即两个过程的特征拉伸率和异质性参数。了解这些参数使我们能够分别构建由自旋标记的旋转扩散决定的自旋晶格弛豫率的概率分布以及严格由与分子氧碰撞引起的弛豫分布。后者的分布由膜内氧扩散浓度乘积的分布决定，这形成了描述膜流动性和非均质性的敏感新方法。该方法在计算机上得到了验证，并通过拟合来自自旋标记的完整核纤维细胞质膜的 SR 信号，该质膜是从用不同空气比例平衡的猪眼晶状体中提取的。