Most of the circulating insulin-like growth factors-I and -II are present in the 150 kDa complex during human pregnancy.
The aim of this study was to assess the molecular size distribution of insulin-like growth factors (IGFs) complexed to IGF-binding proteins (IGFBPs) in serum of non-pregnant and pregnant women. Sera were fractionated on a size-exclusion column at pH 7.4 to resolve different IGF-IGFBP complexes from unbound IGFs. Each fraction was further chromatographed on a size-exclusion column under acid conditions to dissociate IGFs from binding proteins prior to measurement of the IGF content of the complexes. The IGF-containing fractions from the acid column were assayed specifically for IGF-I and IGF-II. Serum pooled from pregnant women contained more IGF-I and IGF-II than serum from non-pregnant women. In both groups most of the IGF-I and IGF-II was found in a large (150 kDa) complex in serum and the remainder was present in complexes eluting in the 40-50 kDa region at pH 7.4. Some free IGF-I was also detected. Serum fractions collected by size-exclusion chromatography at pH 7.4 were also analysed by Western-ligand blotting to characterize the IGFBPs in the two main IGFBP size classes. In serum pooled from non-pregnant women, the 150 kDa IGF-IGFBP complexes contained a 40-50 kDa IGFBP doublet following Western-ligand blot analysis. This IGFBP co-migrated with a pure IGFBP-3 standard. IGFBPs of 34, 28 and 24 kDa all contributed to the 40-50 kDa IGF-IGFBP complexes of the pH 7.4 chromatograph.(ABSTRACT TRUNCATED AT 250 WORDS)
Gargosky
S E
SE
Department of Biochemistry, University of Adelaide, South Australia.
Owens
P C
PC
Walton
P E
PE
Owens
J A
JA
Robinson
J S
JS
Wallace
J C
JC
Ballard
F J
FJ
D015153:Blotting, Western; D002352:Carrier Proteins / Q000097:blood*; D005591:Chemical Fractionation; D002845:Chromatography / Q000379:methods; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D008970:Molecular Weight; D011247:Pregnancy / Q000097:blood*
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II