Complex formation between transcortin and the 20 kDa sialoglycoprotein from the plasma membrane of human decidual endometrium (presumably a transcortin-recognizing subunit of transcortin membranes receptor) was studied using cross-linking reagents. The action of 1,5-difluoro-3,4-dinitrobenzene (DFDNB) on a solution of 125I-labelled 20 kDa sialoglycoprotein and unlabelled transcortin resulted in the formation of two 125I-containing species that corresponded to covalently linked complexes of one transcortin molecule and either 2 or 4 molecules of the labelled membrane sialoglycoprotein. Only the latter complex was observed when the endometrium membranes were incubated with [25I]transcortin and treated with DFDNB. This suggests that the functional form of transcortin-recognizing subunit of the membrane receptor is a tetramer.
