A purified bovine serum albumin preparation contains an insulin-like growth factor (IGF) binding protein-3 fragment that forms ternary complexes selectively with IGF-II and the acid-labile subunit.
Among the six insulin-like growth factor binding proteins (IGFBP), only IGFBP-3 and IGFBP-5 form ternary complexes with IGFs and the acid-labile sunbunit (ALS). In a commercial, highly-purified BSA preparation, ternary complex formation was detected using radio-labeled IGF-II and human serum-derived ALS, with precipitation by ALS antiserum. In contrast, no complexes with radio-labeled IGF-I were detected under the same conditions. Size-fractionation of the BSA on Superose-12 showed the peak of ternary complex forming activity at approximately 30 kDa. To purify the active factor, a solution of the BSA was pumped onto a [Gly(1)]IGF-II affinity column, and eluted fractions were lyophilized and applied to a C18 HPLC column. The eluted fractions showing ternary complex forming activity maintained a preference for IGF-II in forming ternary complexes and a slight preference in forming binary complexes with IGF-II rather than IGF-I. By silver staining after non-reducing SDS-PAGE, the peak activity in the HPLC-eluted fractions appeared as 30 kDa and 21-24 kDa bands. Amino-terminal sequencing of this peak activity revealed bovine IGFBP-3. These results demonstrate that amino-terminal proteolyzed bovine IGFBP-3 is present in a highly purified BSA preparation. In contrast to intact human IGFBP-3 and IGFBP-5, this form of bovine IGFBP-3 forms ternary complexes preferentially with IGF-II rather than IGF-I.
Twigg
S M
SM
Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Pacific Highway, St Leonards, Sydney, NSW 2065, Australia. twiggs@ohsu.edu
Hardman
K V
KV
Baxter
R C
RC
D000818:Animals; D002417:Cattle; D006801:Humans; D066298:In Vitro Techniques; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*
D018972:Insulin-Like Growth Factor Binding Protein 3; D010446:Peptide Fragments; D021122:Protein Subunits; D011994:Recombinant Proteins; D012710:Serum Albumin, Bovine; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II