A 30-kDa fragment of insulin-like growth factor (IGF) binding protein-3 in human pregnancy serum with strongly reduced IGF-I binding

Proteolytic cleavage of insulin-like growth factor (IGF) binding protein (IGFBP)-3 during pregnancy is likely to have both IGF-dependent and -independent effects on maternal, placental and fetal growth and metabolism. A 30-kDa proteolytic IGFBP-3 fragment was isolated from third trimester pregnancy human serum and identified by N- and C-terminal amino acid sequence analysis and mass spectrometry to correspond to residues 1–212 of the parent protein. This fragment is the dominating IGFBP-3 immunoreactive species in pregnancy serum. The 30-kDa fragment was also detected in serum of non-pregnant women where it coexists with intact IGFBP-3. Using biosensor technology, (1–212)IGFBP-3 was found to have 11-fold lower affinity for IGF-I compared to intact IGFBP-3, while a 4-fold decrease in affinity was found for IGF-II. Tests with des(1–3)IGF-I suggest fast binding of IGF-I to the N-terminal region of IGFBP-3 and similar affinity to a slow binding site in the C-terminal region. Received 24 April 2007; received after revision 11 June 2007; accepted 13 June 2007     

Enzyme immunometric assay for the determination of pregnancy associated plasma protein A (PAPP-A) with the antigen as solid phase (conjoint IEMA)

Summary Purified pregnancy associated plasma protein A (PAPP-A) can be effectively bound to polystyrene microtitre plates. This immobilized antigen competes with the added serum PAPP-A of unknown concentration for the limited amount of peroxidase-labeled monospecific anti-PAPP-A antibody incubated simultaneously. The sensitivity is 0.2 WHO unit/ml and non-specific binding is 1.0%.Acknowledgments. My thanks go to the Janggen-Pöhn-Stiftung, St. Gallen, Switzerland, for the reception of a fellowship grant which enabled this work to be carried out. I would also like to thank Arnold Klopper, Professor of Reproductive Endocrinology, for many stimulating discussions, Garry Luke for excellent technical assistance, and the Department of Medical Illustration of the University of Aberdeen for the preparation of the graphics. The donkey serum was generously supplied by the Scottish Antibody Production Unit, Carluke, Lanarkshire.     

Enzyme immunometric assay for the determination of pregnancy associated plasma protein A (PAPP-A) with the antigen as solid phase (conjoint IEMA)

Purified pregnancy associated plasma protein A (PAPP-A) can be effectively bound to polystyrene microtitre plates. This immobilized antigen competes with the added serum PAPP-A of unknown concentration for the limited amount of peroxidase-labeled monospecific anti-PAPP-A antibody incubated simultaneously. The sensitivity is 0.1 WHO unit/ml and non-specific binding is 1.0%.