PURIFICATION AND PROPERTIES OF PLACENTAL PROLACTIN-RELATED PROTEIN-I

We used sucrose density gradient centrifugation, size exclusion chroma tography, and high-pressure reversed-phase chromatography in the purif ication of bovine prolactin-related protein-I (bPRP-I) to homogeneity from a secretory granule-enriched fraction of fetal cotyledon. Amino t erminal sequence was unambiguous, consistent with the nucleic acid seq uence of the cDNA 50 codons distal to the initial AUG in the open read ing frame, and began with the residues: RKSFTDRFMNNAASLSHDFY-. This is distinct from the signal peptide cleavage site predicted by the algor ithm of von Heijne (1986) as well as that expected by comparison with other members of the growth hormone/prolactin family of hormones. The level of bPRP-I in uterine fluid was sufficient to detect by Western b lot of unfractionated material and estimated as at least 0.65 mu M. In contrast, bPRP-I was undetectable in the serum by this method. Intera ction of [I-125]-bPRP-I with high molecular weight serum components in terfered with its measurement by radio-immunoassay, and could be repli cated with purified alpha(2)-macroglobulin with an apparent KD of abou t 0.41 mu M. Thus, the bPRP-I gene product is processed, secreted and distributed in a manner consistent with a paracrine action at the mate rno-fetal interface. (C) 1997 W. Saunders Company Ltd.