Studies on the subunit and polypeptide structure of a polymeric form of pregnancy-specific beta 1-glycoprotein.

The structure of a high-molecular-weight form of Pregnancy-Specific beta 1-Glycoprotein designated PSB1G-I that had been previously isolated from maternal serum was studied by gel chromatography in guanidine hydrochloride dissociating solvent. Evidence was obtained that subunits of identical size (bonded together non-covalently) but of differing polypeptide compositions constitute the PSB1G-I molecule. The subunits of PSB1G-I have been designated alpha and beta subunits. Reduction of PSB1G-I results in an intact alpha chain and two beta chains (beta 1 and beta 2) that are linked in the parent beta subunit by covalent bonds. The collective molecular weights of the alpha, beta 1 and beta 2 chains are equal to 97 800 which is assumed to represent the 'true' molecular weight of 'native' serum PSB1G.