Oligomerization of pregnancy-specific β1-glycoprotein (SP1) at physiologic pH and ionic strength

Abstract Highly purified pregnancy-specific μ 1 -glycoprotein (SP 1 ) migrated in gel electrophoresis as a homogeneous species and behaved as a single species in 6 mol/l guanidinium chloride (GdmCl), both in the ultracentrifuge and HPLC. At physiologic pH and ionic strength, in the absence of GdmCl, SP 1 , existed in the form of oligomers of apparent molecular weights of 40000 to > 300000. The specific activity of these oligomers varied over a 5-fold range. Electrophoretic mobility also varied among SP 1 oligomers, with increasing (α-like) mobility shown by oligomers of increasing molecular size. Oligomerization may explain some or all of the reports of SP 1 heterogeneity.