PHOSPHORYLATION OF INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-1 INCREASES IN HUMAN AMNIOTIC-FLUID AND DECIDUA FROM EARLY TO LATE PREGNANCY

Different fractions of insulin-like growth factor-binding protein-1 (I GFBP-1) from anion exchange chromatography represent differently phosp horylated forms as demonstrated by protein kinase and alkaline phospha tase treatments. The major fraction is non-phosphorylated. Three minor fractions are more phosphorylated and, in native polyacrylamide gel e lectrophoresis (PAGE), they migrate faster than the major fractions. W e studied the changes in phosphorylation of decidual and amniotic flui d IGFBP-1 during pregnancy. Both in decidua and in amniotic fluid the degree of phosphorylation increased from early to late pregnancy, as i ndicated by faster mobility of IGFBP-1 in native PAGE and increased re lative amount of the phosphorylated forms in anion exchange chromatogr aphy. The more phosphorylated forms had higher IGF-binding affinity th an the less phosphorylated forms. As the degree of phosphorylation of IGFBP-1 is highest in full term decidua it is likely that the inhibito ry role of IGFBP-1 is accentuated in the end of pregnancy.