ISOLATION AND PARTIAL CHARACTERIZATION OF A PREGNANCY-ASSOCIATED GLYCOPROTEIN FAMILY FROM THE COAT PLACENTA

Antigen(s) immunologically related to pregnancy-associated glycoprotei ns (PAGs) have previously been detected in the serum of pregnant goats . In this work, we describe a partial characterization of a family of PAGs isolated from the placenta of the goat. The procedure, monitored by RIA, included extraction of proteins at neutral pH, acidic, and amm onium sulfate precipitations; and gel filtration and ion exchange chro matographies. Immunoreactivity, initially located in the acidic supern atant and in the 40-80% ammonium sulfate fractions, was equally apport ioned between the 0.04 and 0.08 M NaCl DEAE fractions. After further p urification of both DEAE fractions, the preparations were subjected to one- and two-dimensional electrophoresis, and individual polypeptides were analyzed by amino acid sequencing. Three PAGs, which differed in amino acid sequence and apparent molecular masses (62, 59, and 55 kDa ), were detected, each containing several isoforms with different pls: caprine (c) PAG62 (pl: 5.1, 4.8), cPAG59 (pl: 6.2, 5.9, 5.6), and cPA G55 (pl: 5.3, 5.1, 4.9). These proteins had high sequence identities t o each other and to PAGs purified from other species. Each had two put ative N-glycosylation sites within the 27 amino terminal residues sequ enced. This work demonstrates that PAGs are present in goat placenta a nd that multiple forms are expressed.