High molecular weight insulin-like growth factor binding protein complex. Purification and properties of the acid-labile subunit from human serum.
In the human circulation, the insulin-like growth factors (IGFs) circulate as part of a growth hormone-dependent 125- to 150-kDa complex. This complex has been postulated to contain, in addition to IGFs and one or more IGF-binding proteins, an acid-labile subunit (ALS) which does not itself bind IGFs. In this study, the ALS has been purified 1600-fold from human serum, and its binding properties have been examined. Fresh serum was fractionated on DEAE-Sephadex, and active fractions (determined by radioimmunoassay) were purified by affinity chromatography on an IGF-agarose column saturated with the plasma IGF-binding protein BP-53. After further high performance anion exchange chromatography, an ALS preparation was obtained which contained only an 84-86-kDa protein doublet, converting to a single 70-kDa band on N-glycanase treatment, and having an amino-terminal sequence unrelated to IGF-binding proteins or receptors. Pure ALS formed a complex with BP-53 (Ka approximately 5 x 10(8) M-1), immunoprecipitable by anti-BP-53 antiserum, only in the presence of IGF-I or IGF-II. This complex appeared at approximately 150 kDa on high performance gel chromatography. Pure ALS had no intrinsic IGF-binding activity and no effect on the binding of IGF-I or IGF-II to BP-53. These studies suggest that formation of the high molecular weight IGF-binding protein complex requires ALS, BP-53, and IGF.
Baxter
R C
RC
Department of Endocrinology, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.
Martin
J L
JL
Beniac
V A
VA
D002352:Carrier Proteins / Q000302:isolation & purification* / Q000502:physiology; D002853:Chromatography, Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D008970:Molecular Weight; D011863:Radioimmunoassay; D013002:Somatomedins / Q000302:isolation & purification* / Q000502:physiology
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins