Immunochemical and biochemical relationship between human pregnancy-associated secreted endometrial alpha 1- and alpha 2-globulins (alpha 1- and alpha 2-PEG) and the soluble placental proteins 12 and 14 (PP12 and PP14).

Two proteins, pregnancy-associated endometrial alpha 1- and alpha 2-globulins (alpha 1- and alpha 2-PEG), synthesized de novo and secreted by the human endometrium and decidua during pregnancy, have been demonstrated to be immunochemically related to the soluble placental proteins PP12 and PP14 isolated from term placenta. However, although these immunochemically similar endometrially- and placentally-derived proteins differ in their reported biochemical properties, in this report we have demonstrated that PP12 and PP14 are biochemically identical to alpha 1- and alpha 2-PEG with respect to subunit size. We conclude that these placental proteins are derived from the endometrium by de novo synthesis, and we suggest that the localization of these proteins to the placenta reflects either absorption, specific binding or processing by the trophoblast. The significance of clinical studies involving PP12 and PP14 measurement must therefore be reassessed in the light of their exclusive endometrial origin.