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JONATHAN N. SOUTHARD, FRANK TALAMANTES, High Molecular Weight Forms of Placental Lactogen: Evidence for Lactogen-Macroglobulin Complexes in Rodents and Humans, Endocrinology, Volume 125, Issue 2, 1 August 1989, Pages 791–800, https://doi.org/10.1210/endo-125-2-791
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Abstract
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 PLII in plasma had a Mr of 360,000 by sodium dodecyl sulfatepolyacrylamide 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 α2-macroglobulin. The most prominent circulating high Mr form of hamster PL-II had a Mr similar to that of α2-macroglobulin by both gel filtration and SDS-PAGE. In addition, it had a mobility similar to that of α2-macroglobulin on nondenaturing polyacrylamide gels, and it was about 10% asparagine-linked carbohydrate by weight, as is α2-macroglobulin. These similarities and the ability of hamster PL-II to form a disulfide-bonded complex with α2-macroglobulin in vitro suggest that the major circulating form of PL-II in the hamster may be a disulfidebonded complex of one or more PL monomers with α2-macroglobulin or a related plasma protein. Similar complexed forms of PL may be present in mice and humans.
