Purification and Partial Characterization of Two Prolactin-Like Glycoprotein Hormone Complexes from the Midpregnant Mouse Conceptus*

Publisher Website
Google Scholar
Abstract
Two PRL-like glycoprotein hormone complexes were purified from the medium of cultured mouse comceptuses from day 10 of pregnancy: mouse placental lactogen-I (mPL-I) (29-32K), and mPL-I (36.5-42K). Sodium dodecyl sulfate-gel electrophoresis revealed that mPL-I (36.5-42K) is a complex of five proteins with mol wt of 36.5K, 37.5K, 39K, 40.5K, and 42K. Deglycosylation with peptide N-glycosidase F or trifluoromethanesulfonic acid produced a single 29K protein, mPL-I (36.5-42K) was also sensitive to neuraminidase, but not to endo-.beta.-N-acetylglucosaminidase H or bacterial alkaline phosphatase. The production of intermediates from partial digestion of mPL-I (36.5-42K) with endo-.beta.-N-acetylglucosaminidase F indicated the presence of multiple glycosylation sites. mPL-1 (29-32K) is a complex of three proteins with mol wt of 29K, 30.5K, and 32K. Treatment with peptide:N-glycosidase F or trifluoromethanesulfonic acid reduced the mol wt of the 30.5K and 32K bands to 28K. The 30.5K band was sensitive to endo-.beta.-N-acetylglucosaminidase H and endo-.beta.-N-acetylglucosaminidase F, but the 32K band was not. Neither band was sensitive to neuraminidase or bacterial alkaline phosphatase. The 29K band was resistant to all chemical and enzymatic treatments and is probably not glycosylated or phosphorylated. In the nonreduced state, neither form of mPL-I showed an increase in mobility over that of its reduced counterpart on sodium dodecyl sulfate-gel electrophoresis, indicating that neither form of mPL-I contains the large disulfide loop common to hormones of the PRL family. After iodination, all component proteins of both forms of mPL-I were found to bind to day 17 pregnant mouse liver membranes and were displaceable by excess mPL-II. In a radioreceptor assay, 125I-labeled mPL-I (36.5-42K) was displaced by mPRL or mPL-II, but not by mGH. An antiserum to both forms of mPL-I was generated, and a RIA employing mPL-I (36.5-42K) as the standard and radioligand was developed. Dilutions of day 10 pregnant maternal mouse serum and placental homogenate and a partially purified fraction of mPL-I (29-32K) produced displacement curves parallel to that of mPL-I (36.5-42K) standard curve. Five micrograms of mPRL, mPL-II, or mGH or 10 .mu.l day 17 pregnant or male mouse serum did not displace the radioligand from the antibody, mPL-1 (36.5-42K) was lactogenic, but it did not posess LH-like bioactivity.