London R E, Gabel S A
Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Biophys J. 1995 Nov;69(5):1814-8. doi: 10.1016/S0006-3495(95)80051-2.
Fluorine-19 magnetization transfer studies have been used to measure the transport rate of glucopyranosyl fluorides under equilibrium exchange conditions. Although rate constants and permeabilities could be determined for beta-D-glucopyranosyl fluoride, the exchange rate for alpha-D-glucopyranosyl fluoride was found to be too slow for determination using this method. The time-dependent decomposition of the beta-glucopyranosyl fluoride also limits the accuracy of the numerical results for this species; however, it is clear that the permeabilities of the alpha and beta forms differ significantly, i.e., P beta > P alpha. This observation is in contrast to recent observations for n-fluoro-n-deoxyglucose, for which P alpha > P beta for n = 2, 3, 4, or 6. The difference can be explained in terms of a simple alternating conformation model in which one of the conformations (with an external sugar-binding site) exhibits a preference for the beta form of the molecule, while the second conformation (with an internal sugar binding site) exhibits a preference for the alpha form. Fluorine/hydroxyl substitutions unmask these preferences by selectively reducing the binding to one of the conformations, depending on the specific site of fluorination.
氟 - 19 磁化转移研究已被用于测量平衡交换条件下吡喃葡萄糖基氟化物的转运速率。尽管可以确定β - D - 吡喃葡萄糖基氟化物的速率常数和渗透率，但发现α - D - 吡喃葡萄糖基氟化物的交换速率太慢，无法用此方法测定。β - 吡喃葡萄糖基氟化物随时间的分解也限制了该物种数值结果的准确性；然而，很明显，α型和β型的渗透率有显著差异，即Pβ > Pα。这一观察结果与最近对n - 氟 - n - 脱氧葡萄糖的观察结果相反，对于n = 2、3、4或6的n - 氟 - n - 脱氧葡萄糖，Pα > Pβ。这种差异可以用一个简单的交替构象模型来解释，其中一种构象（具有外部糖结合位点）对分子的β型表现出偏好，而第二种构象（具有内部糖结合位点）对α型表现出偏好。氟/羟基取代通过根据氟化的特定位点选择性地减少与一种构象的结合来揭示这些偏好。
