High molecular weight forms of placental lactogen: evidence for lactogen-macroglobulin complexes in rodents and humans.
Gel filtration chromatography of maternal plasma from late pregnant hamsters demonstrated that approximately 90% of hamster placental lactogen-II (PL-II) is present as high mol wt (Mr) forms. A major peak of immunoactive hamster PL-II with a Mr of 600,000 and a smaller peak (Mr, 210,000) were observed. The major high Mr form of hamster PL-II in plasma had a Mr of 360,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). High Mr forms also predominate in placental extracts, but differ from the plasma forms. 125I-Labeled monomeric hamster PL-II (Mr, 22,000) formed a disulfide-bonded complex (Mr, 720,000 by gel filtration and 360,000 by SDS-PAGE) when incubated in vitro with serum of male, nonpregnant female, or pregnant hamsters. The in vitro complex was also formed with unlabeled hamster PL-II. Similar high Mr complexes were formed, but to a lesser extent, when 125I-labeled mouse PL-II and human PL were incubated with the homologous late pregnant serum. High Mr complexes (Mr, 360,000 by SDS-PAGE) were also formed when the three 125I-labeled PLs were incubated with purified human alpha 2-macroglobulin. The most prominent circulating high Mr form of hamster PL-II had a Mr similar to that of alpha 2-macroglobulin by both gel filtration and SDS-PAGE. In addition, it had a mobility similar to that of alpha 2-macroglobulin on nondenaturing polyacrylamide gels, and it was about 10% asparagine-linked carbohydrate by weight, as is alpha 2-macroglobulin. These similarities and the ability of hamster PL-II to form a disulfide-bonded complex with alpha 2-macroglobulin in vitro suggest that the major circulating form of PL-II in the hamster may be a disulfide-bonded complex of one or more PL monomers with alpha 2-macroglobulin or a related plasma protein. Similar complexed forms of PL may be present in mice and humans.
Southard
J N
JN
Department of Biology, University of California, Santa Cruz 95064.
Talamantes
F
F
D000818:Animals; D002850:Chromatography, Gel; D006224:Cricetinae; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D008259:Macroglobulins / Q000032:analysis / Q000378:metabolism*; D008647:Mesocricetus; D051379:Mice; D008815:Mice, Inbred Strains; D008970:Molecular Weight; D010920:Placenta / Q000378:metabolism; D010928:Placental Lactogen / Q000032:analysis* / Q000378:metabolism; D011247:Pregnancy
D008259:Macroglobulins; D010928:Placental Lactogen