CHARACTERIZATION OF PROTEIN-PRODUCTION BY CAPRINE PLACENTAL MEMBRANES- IDENTIFICATION AND IMMUNOLOCALIZATION OF RETINOL-BINDING PROTEIN

Caprine chorion, allantois and amnion from days 23, 28, 35, 39 and 45, and yolk sac from day 23 of pregnancy were isolated by dissection and cultured for 24 h in modified minimum essential medium in the presenc e of [S-35] methionine. De novo-synthesized proteins released into the culture medium were analyzed by two-dimensional PAGE and fluorography . Patterns of protein production by these isolated extraembryonic memb ranes remained relatively unchanged from days 23 to 45 of pregnancy. E lectrophoretic profiles of proteins synthesized by allantois and amnio n were identical but distinct from that produced by chorion. Yolk sac was the major source of serum-like proteins. An acidic (pI 5.3-6.3) 22 kDa protein, which consisted of four isoelectric variants, was produc ed by all extraembryonic membranes and demonstrated to immunoreact wit h antiserum produced against bovine placental retinol-binding protein (REP). Limited N-terminal sequence analysis of one major isoform indic ated that the protein had complete homology with bovine REP over the f irst 15 amino acids. Immunoreactive REP was localized in epithelial ce lls lining the chorion, allantois and amnion. In this study, we have c haracterized and compared protein production by isolated extraembryoni c membranes through days 23 to 45 of pregnancy and identified the 22 k Da protein as caprine REP of placental origin.