Benesch R E, Kwong S, Benesch R, Baugh C M
J Biol Chem. 1985 Nov 25;260(27):14653-8.
A binding method that detects only the strongest binding site for a ligand on a protein has been used to show that folates and folate analogs, conjugated with poly-gamma-glutamates, are bound to hemoglobin. When the concentration of hemoglobin is much larger than that of the polyglutamate, as is the case in the red cell, the fraction bound is a direct function of the hemoglobin concentration and is independent of the total polyglutamate concentration. Binding to deoxyhemoglobin tetramers is competitive with 2,3-diphosphoglycerate. In oxyhemoglobin the folyl and methotrexate polyglutamates are bound preferentially by free alpha beta dimers, but removal of the pteridine moiety leads to tetramer binding even in oxyhemoglobin. Changes in the length of the polyglutamate side chain and alterations of the pteridine structure such as reduction and/or methylation have a much larger effect on the constant for binding to deoxyhemoglobin tetramers than on that for oxyhemoglobin dimers. The implications of these results for the storage of pteroylpolyglutamates in the erythrocyte and their release from the red cell under the influence of the degree of oxygenation and variations in the 2,3-diphosphoglycerate level are discussed.
一种仅检测配体在蛋白质上最强结合位点的结合方法已被用于表明，与聚γ-谷氨酸缀合的叶酸和叶酸类似物与血红蛋白结合。当血红蛋白浓度远高于聚谷氨酸浓度时，如在红细胞中那样，结合分数是血红蛋白浓度的直接函数，且与总聚谷氨酸浓度无关。与脱氧血红蛋白四聚体的结合与2,3-二磷酸甘油酸具有竞争性。在氧合血红蛋白中，叶酸和甲氨蝶呤聚谷氨酸优先被游离的αβ二聚体结合，但去除蝶啶部分即使在氧合血红蛋白中也会导致四聚体结合。聚谷氨酸侧链长度的变化以及蝶啶结构的改变，如还原和/或甲基化，对与脱氧血红蛋白四聚体结合常数的影响比对氧合血红蛋白二聚体结合常数的影响大得多。讨论了这些结果对于红细胞中蝶酰聚谷氨酸的储存及其在氧合程度和2,3-二磷酸甘油酸水平变化影响下从红细胞释放的意义。
