The human intermediate-affinity interleukin 2 receptor consists of two distinct, partially homologous glycoproteins.

In this report we demonstrate that the human intermediate-affinity-type interleukin (IL) 2 receptor (IL 2R) consists of two distinct glycoproteins designated H1 and H2, whereas the high-affinity IL 2R consists of three chains, H1, H2 and the light chain (L), the Tac antigen. They are neither linked by disulfide bridges to each other nor to the L chain. Similar to the L chain, H1 and H2 apparently carry intramolecular disulfide bonds. From affinity-labeled IL 2 intermediate-affinity receptor complexes, we deduced an apparent mol. mass of 70 kDa for H1 and of 75 kDa for H2 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and of 55 kDa for H1 and of 85 kDa for H2 in SDS-PAGE/urea. As demonstrated by limiting proteolysis, both glycoproteins display high homologies or even identity proximal to the IL 2-binding sites. The areas which are responsible for the striking differences between H1 and H2 in SDS-PAGE/urea are located distally to the IL2-binding site and, in contrast to the L chain, are protected from the action of exogenous proteases by the plasma membrane.