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Circulating levels and molecular distribution of the acid-labile (alpha) subunit of the high molecular weight insulin-like growth factor-binding protein complex. 1990

R C Baxter
Department of Endocrinology, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia.

A RIA is described for the acid-labile (alpha) subunit of the high mol wt insulin-like growth factor (IGF)-binding protein complex, a glycoprotein of approximately 85,000 daltons (approximately 85K) which combines with the GH-dependent binding protein (BP-53 or IGFBP-3) and IGF-I or IGF-II to form the complex. The assay shows relative specificity for higher primate species. Whereas amniotic fluid, cerebrospinal fluid, and seminal plasma contain virtually no immunoreactive alpha-subunit, the protein is easily detectable in 0.5-microL serum samples. Serum alpha-subunit levels are markedly age dependent, rising over 5-fold from birth to puberty, then remaining relatively constant throughout adulthood. In 170 children, there was a strong association between alpha-subunit and IGFBP-3 levels. Mean alpha-subunit levels (+/- SD) in adults were 24.2 +/- 4.7 mg/L in 93 normal subjects, 54.1 +/- 15.5 mg/L in 12 acromegalics, 6.5 +/- 4.8 mg/L in 10 GH-deficient subjects, and 31.5 +/- 5.7 mg/L in 18 third term pregnant women. In serum fractionated by gel chromatography, alpha-subunit appeared as a broad 100-150K peak. After depleting serum samples of IGFBP-3 by immunoaffinity chromatography, approximately one third of alpha-subunit remained, in a peak of about 100K, suggesting that two thirds of the total alpha-subunit in serum is present in the approximately 150K complex, and one third is uncomplexed. Development of this RIA for alpha-subunit will allow further study of regulation of the GH-dependent complex.

UI MeSH Term Description Entries
D007223 Infant A child between 1 and 23 months of age. Infants
D007231 Infant, Newborn An infant during the first 28 days after birth. Neonate,Newborns,Infants, Newborn,Neonates,Newborn,Newborn Infant,Newborn Infants
D007334 Insulin-Like Growth Factor I A well-characterized basic peptide believed to be secreted by the liver and to circulate in the blood. It has growth-regulating, insulin-like, and mitogenic activities. This growth factor has a major, but not absolute, dependence on GROWTH HORMONE. It is believed to be mainly active in adults in contrast to INSULIN-LIKE GROWTH FACTOR II, which is a major fetal growth factor. IGF-I,Somatomedin C,IGF-1,IGF-I-SmC,Insulin Like Growth Factor I,Insulin-Like Somatomedin Peptide I,Insulin Like Somatomedin Peptide I
D007335 Insulin-Like Growth Factor II A well-characterized neutral peptide believed to be secreted by the LIVER and to circulate in the BLOOD. It has growth-regulating, insulin-like and mitogenic activities. The growth factor has a major, but not absolute, dependence on SOMATOTROPIN. It is believed to be a major fetal growth factor in contrast to INSULIN-LIKE GROWTH FACTOR I, which is a major growth factor in adults. IGF-II,Multiplication-Stimulating Activity,Somatomedin MSA,IGF-2,Insulin Like Growth Factor II,Insulin-Like Somatomedin Peptide II,Multiplication-Stimulating Factor,Somatomedin A,Factor, Multiplication-Stimulating,Insulin Like Somatomedin Peptide II,Multiplication Stimulating Activity,Multiplication Stimulating Factor
D008297 Male Males
D008875 Middle Aged An adult aged 45 - 64 years. Middle Age
D008970 Molecular Weight The sum of the weight of all the atoms in a molecule. Molecular Weights,Weight, Molecular,Weights, Molecular
D011247 Pregnancy The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH. Gestation,Pregnancies
D011863 Radioimmunoassay Classic quantitative assay for detection of antigen-antibody reactions using a radioactively labeled substance (radioligand) either directly or indirectly to measure the binding of the unlabeled substance to a specific antibody or other receptor system. Non-immunogenic substances (e.g., haptens) can be measured if coupled to larger carrier proteins (e.g., bovine gamma-globulin or human serum albumin) capable of inducing antibody formation. Radioimmunoassays
D002352 Carrier Proteins Proteins that bind or transport specific substances in the blood, within the cell, or across cell membranes. Binding Proteins,Carrier Protein,Transport Protein,Transport Proteins,Binding Protein,Protein, Carrier,Proteins, Carrier

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