During purification, insulin-like growth factor binding protein-1 from
amniotic fluid was separated into five different peaks by anion excha
nge chromatography.1 These peaks represent differently phosphorylated
forms of IGFBP-1. The major peak (peak 1) is non-phosphorylated. Peaks
3, 4, and 5 are more phosphorylated and, in native polyacrylamide gel
electrophoresis (PAGE), they migrate faster than peaks 1 and 2. The m
ore phosphorylated forms have higher IGF-I-binding affinity. Both deph
osphorylated and phosphorylated peaks enhanced IGF-I stimulated DNA-sy
nthesis in fetal skin fibroblast cell culture. They, however, inhibite
d the binding of IGF-I to the same cells. The phosphorylation of IGFBP
-1 was changed during pregnancy. 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 more phosphorylated peaks in anion exchange chrom
atography. Human ovarian follicular fluid, culture media from human gr
anulosa cells and endometrial adenocarcinoma cells (HEC-1-B) consisted
mostly of the non-phosphorylated form of IGFBP-1.