Molecular characterization of pregnancy-associated plasma protein-A by electrophoresis

Gradient polyacrylamide gel electrophoresis, isoelectric focusing and multidimensional immunoelectrophoretic techniques have been applied in order to physicochemically characterize pregnancy‐associated plasma protein‐A (PAPP‐A). By lectin affinity immunoelectrophoresis, PAPP‐A contained sialic acid, glucose/mannose and N‐acetyl‐α‐D‐galactosamine. Immunoelectrophoretic analyses after incubation with various glycolases confirmed these findings and demonstrated that PAPP‐A contained glucuronic acid, perhaps in chondroitin sulphate moities, thus indicating that PAPP‐A may be a proteoglycan rather than a glycoprotein. Analysis by metal chelate and dye ligand affinity immunoelectrophoresis demonstrated many similarities between PAPP‐A and α2‐macroglobulin (α2M). However, unlike α2M, PAPP‐A did not form immunologically reactive complexes when incubated with proteases. Furthermore, as demonstrated by autoradiographic studies, PAPP‐A did not contain internal thiolester groups, thus indicating that PAPP‐A cannot inhibit proteases by molecular entrapment and, despite the homotetrameric molecular conformation, PAPP‐A and α2M may not have evolved from a common ancestral protein.