Sen I
Biochim Biophys Acta. 1985 Feb 28;813(1):103-10. doi: 10.1016/0005-2736(85)90350-5.
Radiolabelled angiotensin II binds to a single class of high-affinity binding sites on purified rabbit hepatic membranes. The binding is specific, reversible and saturable. Displacement studies using angiotensin and various analogs of angiotensin II disclosed a structure-activity profile similar to that found in physiologically relevant angiotensin II receptor sites. Treatment of membranes with the reducing agent, dithiothreitol, causes a significant decrease in the affinity of angiotensin II binding sites for the native ligand. This effect is mimicked by a 15-fold higher concentration of the monosulfhydryl derivative, 2-mercaptoethanol. Kinetic studies also indicated that dithiothreitol increases the rate of dissociation of bound ligand from the membrane without significantly affecting the association rate. In contrast, treatment of membranes with the metal chelators, ethylenediaminetetracetic acid (EDTA) and ethyleneglycol bis(beta-aminoethyl ether)-N,N'-tetracetic acid (EGTA), does not affect the binding of radiolabeled angiotensin II. Furthermore, dithiothreitol inhibited the binding of angiotensin II to a solubilized partially purified preparation of angiotensin II-binding protein from the same tissue and also increased the dissociation of bound angiotensin II. This indicates that the effect of the sulfhydryl reagents on the membrane binding sites is the result of a direct alteration of the binding sites rather than a gross modification of the structure of the membrane.
放射性标记的血管紧张素II与纯化的兔肝细胞膜上的一类高亲和力结合位点相结合。这种结合具有特异性、可逆性和饱和性。使用血管紧张素和血管紧张素II的各种类似物进行的置换研究揭示了一种与在生理相关的血管紧张素II受体位点中发现的结构-活性概况相似的情况。用还原剂二硫苏糖醇处理细胞膜会导致血管紧张素II结合位点对天然配体的亲和力显著降低。这种效应可被单巯基衍生物2-巯基乙醇浓度高15倍的情况所模拟。动力学研究还表明，二硫苏糖醇增加了结合配体从膜上解离的速率，而对结合速率没有显著影响。相比之下，用金属螯合剂乙二胺四乙酸（EDTA）和乙二醇双（β-氨基乙醚）-N,N'-四乙酸（EGTA）处理细胞膜不会影响放射性标记的血管紧张素II的结合。此外，二硫苏糖醇抑制了血管紧张素II与来自同一组织的可溶部分纯化的血管紧张素II结合蛋白制剂的结合，并且还增加了结合的血管紧张素II的解离。这表明巯基试剂对膜结合位点的作用是结合位点直接改变的结果，而不是膜结构的总体改变。
