Thomson A B
J Membr Biol. 1979 May 7;47(1):39-57. doi: 10.1007/BF01869046.
In the presence of an intestinal unstirred water layer, the relationship between substrate concentration (C1) and unidirectional flux (Jd) is not described by the equation for a rectangular hyperbole. Accordingly, transformations of the Michaelis-Menten equation may not necessarily be linear and may lead to serious errors in the estimation of the affinity constant (Km) and maximal transport rate (Jdm) of carrier-mediated processes. An equation has previously been derived which described Jd under conditions of varying effective thickness or surface area of the unstirred water layer, the free diffusion coefficient of the probe molecule, and the distribution of transport sites along the villus. These theoretical curves have been analyzed by using the Eadie-Hofstee transformation (Jd vs. Jd/C1) of the Michaelis-Menten equation. Use of this plot leads to serious discrepancies between the true and apparent affinity constants and between true and apparent maximal transport rates. These differences are further magnified by failure to correct for the contribution of passive permeation. The Eadie-Hofstee plot is of use, however, to infer certain qualitative characteristics of active transport processes, such as the variation in affinity constants and overlying resistance of the unstirred water layer at different sites along the villus and to predict the adequacy of the correction for the contribution of passive permeation.
在存在肠道未搅动水层的情况下，底物浓度（C1）与单向通量（Jd）之间的关系并非由矩形双曲线方程描述。因此，米氏方程的变换不一定是线性的，可能会在载体介导过程的亲和常数（Km）和最大转运速率（Jdm）估计中导致严重误差。先前已推导了一个方程，该方程描述了在未搅动水层的有效厚度或表面积变化、探针分子的自由扩散系数以及沿绒毛的转运位点分布的条件下的Jd。这些理论曲线已通过使用米氏方程的伊迪-霍夫斯泰变换（Jd对Jd/C1）进行分析。使用此图会导致真实亲和常数与表观亲和常数之间以及真实最大转运速率与表观最大转运速率之间出现严重差异。由于未能校正被动渗透的贡献，这些差异会进一步放大。然而，伊迪-霍夫斯泰图可用于推断主动转运过程的某些定性特征，例如沿绒毛不同位点的亲和常数变化和未搅动水层的上层阻力，并预测被动渗透贡献校正的充分性。
