Saito Y, Sabe H, Suzuki N, Kondo S, Ogura T, Shimizu A, Honjo T
Department of Medical Chemistry, Kyoto University Faculty of Medicine, Japan.
J Exp Med. 1988 Nov 1;168(5):1563-72. doi: 10.1084/jem.168.5.1563.
The IL-2-R is composed of at least two proteins, that is, a 55-kD protein (p55, the L chain, or Tac) and a 75-kD protein (p75, the H chain, or converter). The high affinity binding of IL-2 results in the formation of the ternary complex consisting of IL-2, and the L and H chains. To distinguish the affinity conversion model and the binary complex model we have carried out kinetic studies on the IL-2 binding to the high affinity IL-2-R on T lymphocytes expressing various numbers of L chains and a relatively constant number of H chains. We found that expression of a larger number of L chains accelerated the association of IL-2 to the high affinity receptor. The results are not compatible with the binary complex model that assumes a fixed number of high affinity sites determined by the numbers of a limiting chain. Instead, the results are consistent with the prediction of the affinity conversion model that assumes association of IL-2 to the L chain as the first step of the ternary complex formation and they indicate that the possible role of excess L chains is to accelerate the formation of the ternary complex. The reaction rate constants calculated from the affinity conversion model were reasonably constant.
白细胞介素-2受体（IL-2-R）至少由两种蛋白质组成，即一种55kD的蛋白质（p55，轻链或Tac）和一种75kD的蛋白质（p75，重链或转换蛋白）。IL-2的高亲和力结合导致由IL-2以及轻链和重链组成的三元复合物的形成。为了区分亲和力转换模型和二元复合物模型，我们对IL-2与表达不同数量轻链和相对恒定数量重链的T淋巴细胞上的高亲和力IL-2-R的结合进行了动力学研究。我们发现，大量轻链的表达加速了IL-2与高亲和力受体的结合。这些结果与二元复合物模型不相符，二元复合物模型假定由一条限制链的数量决定固定数量的高亲和力位点。相反，这些结果与亲和力转换模型的预测一致，该模型假定IL-2与轻链的结合是三元复合物形成的第一步，并且它们表明过量轻链的可能作用是加速三元复合物的形成。根据亲和力转换模型计算的反应速率常数相当恒定。
