The major serum protein of fetal and newborn pigs: biochemical properties and identification as a fetal form of alpha 1-acid glycoprotein.

The major protein component of fetal pig serum, has been immunologically identified as alpha 1-acid glycoprotein (orosomucoid). Amino acid composition and total carbohydrate content (around 38% by weight) were similar in the adult and fetal forms of alpha 1-acid glycoprotein. These forms differ, however, in the proportion of individual monosaccharides. Fucose, represented the 1.5% (by weight) in the fetal protein, and the 2.5% in its adult counterpart. The latter was more susceptible to neuraminidase and also possesses a higher mannose/galactose ratio than the fetal form. Insolubilized Concanavalin A (Con A) retained 80% of the adult protein, whereas the fetal form was mostly Con A-non reactive. The proportion of this -non reactive fraction, as revealed by crossed immuno-affino-electrophoresis experiments, was age-dependent and varied from 62% at fetal age of 50-60 days to 80% at birth.