Purification and characterization of the acid-labile subunit of rat serum insulin-like growth factor binding protein complex.
Circulating insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), when occupied by IGF-I or IGF-II, combines with an acid-labile glycoprotein subunit (ALS) to form a high molecular weight complex. In this study, ALS from rat serum has been purified and its properties investigated. Purification involved ion-exchange chromatography, and affinity chromatography on an IGF-I-IGFBP-3 column, yielding almost 1 mg ALS from 100 ml serum. Amino-terminal sequencing confirmed the prediction from previous complementary DNA analysis but indicated that the protein may circulate in a truncated form. Rat ALS was almost as potent as human ALS in binding to human IGF-I-IGFBP-3 complex (association constant, 2.3 nM-1). A sensitive RIA was developed, with high specificity for rodent ALS. Serum ALS rose from 3 micrograms/ml in 2-day-old rats to more than 40 micrograms/ml at 10 weeks, with no sex difference. GH-deficient rats showed 60-75% lower values than controls. This study shows rat ALS to have similar binding properties, and age and GH dependence, to human ALS. The new RIA will facilitate studies of IGF and IGFBP regulation in the rat.
Baxter
R C
RC
Department of Endocrinology, Royal Prince Alfred Hospital, Sydney, New South Wales, Australia.
Dai
J
J
D000375:Aging / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D015292:Glycoprotein Hormones, alpha Subunit / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism*; D013006:Growth Hormone / Q000494:pharmacology; 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; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012737:Sex Factors
D002352:Carrier Proteins; D015292:Glycoprotein Hormones, alpha Subunit; D018969:Insulin-Like Growth Factor Binding Proteins; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone