Large (>160 kDa) Glycoproteins with electrophoretic mobility of Alpha-Globulins, found in high concentration in the Plasma of Pregnant Women but also in a number of species including Mouse, rat, and others (alpha-Macroglobulins). In Humans, they are always present in the circulation and are nonspecific inhibitors of Proteinases, similar to Complement Proteins (C3; C4; C5).