Purification, characterization, and biological compartmentalization of ratfetal antigen 1

This study has established the rat as an animal model for the analysis of t he biological role of fetal antigen 1 (FA1), a protein previously described in humans and mice. FA1 was purified from rat amniotic fluid by immunospec ific affinity chromatography. Immunochemical identity between mouse and rat FA1 was established by crossed tandem immunoelectrophoresis. Molecular siz e was analyzed by mass spectrometry (33 kDa). The amino acid composition wa s determined, and the amino acid sequence was analyzed. The overall amino a cid composition and sequence of the 28 first N-terminal amino acids were id entical to the corresponding parts of rat preadipocyte factor 1 and rat adr enal zone glomerulosa protein. Extensive sequence similarity was found betw een rat and mouse FA1 (86%) and between rat and human FA1 (82%). The concen tration of FA1 in fetal serum, maternal serum, urine, and amniotic fluid in rats was determined using an ELISA. The highest concentrations were found in fetal serum and amniotic fluid around Day 18 of pregnancy. This is the f irst report on the physicochemical characteristics and compartmentalization of rat FA1.