Extensive polymorphism of glycine-rich ß-glycoprotein (GBG) was found in human sera. In all instances, GBG consisted of at least five components on electrophoresis. Patterns were such that they provided evidence for four alleles (at a locus designated Gb) which were expressed as autosomal codominant traits. GbS and GbF were found in all populations but with different frequencies, GbF1 was found in Negroes, and GbS1 was found in Caucasians.
From electrophoretic studies of GBG, evidence was obtained that suggested that the GBG molecule was a tetramer consisting of A and B subunits in a proportion of about 1.6:1. The genetically controlled differences in GBG embodied in the Gb system indicated the presence of a third moiety of the molecule (C), possibly a polypeptide subunit. Electrophoretic studies of fragments from defined types of GBG suggested that GBG cleavage induced by complement or properdin activation in serum occurred through this C moiety, since two variants were detectable in one fragment and two were found in the other fragment.
On comparison of fetal-maternal Gb types, approximately one-half the pairs showed differences. This indicated that GBG did not cross the placental barrier.