OVINE ALLANTOIC FLUID CONTAINS HIGH-CONCENTRATIONS OF ACTIVIN A - PARTIAL DISSOCIATION OF IMMUNOACTIVITY AND BIOACTIVITY

In a preliminary study, allantoic fluid collected from pregnant sheep across gestational ages of 20-124 days contained significantly higher levels of activin bioactivity (189 +/- 74 ng/ml, mean +/- SE) than did amniotic fluid (3.2 +/- 0.6 ng/ml). Using a combination of chromatogr aphy steps, we isolated from 5 L of allantoic fluid approximately 612 mu g of immunoactive activin, which eluted over 10 fractions from a C8 reversed-phase column. When these fractions were assayed in a rat pit uitary cell culture bioassay, in a specific RIA, and in an activin A t wo-site ELISA, the RIA activity was skewed to the less hydrophobic sid e of the activin profile, while the bioactivity was skewed to the more hydrophobic forms. The activity measured in the two-site ELISA more c losely matched the mass of activin as determined by laser densitometry . Amino-terminal sequencing of fractions containing either peak immuno activity or bioactivity showed each to be identical to activin A. This was confirmed by internal sequences from a fraction that eluted in th e area of overlapping immunoactivity and bioactivity. A peptide contai ning at least 18 amino acids at its amino terminus, which were identic al to the conserved region of the acute-phase protein serum amyloid A, was identified in the most immunoactive activin fractions.