N-terminal amino acid sequence of human pregnancy-associated endometrial alpha 1-globulin, an endometrial insulin-like growth factor (IGF) binding protein--evidence for two small molecular weight IGF binding proteins.

We have previously demonstrated that quantitatively the major secretory protein of the human endometrium from the latter half of the first trimester of pregnancy, pregnancy-associated endometrial alpha 1-globulin (alpha 1-PEG), is a small mol wt insulin-like growth factor binding protein (IGF BP) and is detected at high levels in amniotic fluid. N-terminal amino acid sequences have been determined for this protein purified from both these sources and a single N-terminal amino acid sequence Ala Pro Trp Gln Cys Ala Pro Cys Ser Ala Glu Lys Leu Ala Leu Pro Pro was obtained. The first ten residues are identical to those previously reported for the small mol wt IGF BP isolated from amniotic fluid and HEPG2 culture medium. However it was different to that reported for the IGF BP isolated from term placenta, placental protein 12 (PP12), a protein previously suggested to originate in the endometrium. These data suggest that at least two distinct forms of the small mol wt IGF BP exist and supports the hypothesis that the amniotic fluid form originates from the pregnancy endometrium.