Purification and characterization of a unique high molecular weight form of insulin-like growth factor II.
A form of insulin-like growth factor II (IGF-II) with a mol wt of 15,000 has been purified to homogeneity from human Cohn fraction IV1-4. This protein has an amino-terminal sequence through the first 28 residues that is identical to 7.5K IGF-II. The amino acid composition of 15K IGF-II, however, indicates that its carboxyl-terminal region may be different from that predicted from the analysis of IGF-II cDNA clones. The affinities of 15K IGF-II for receptors on rat placental membranes and for an IGF-binding protein that was isolated from the medium of cultured buffalo rat liver cells were similar to those of the 7.5K form of the growth factor. A best-fit analysis of data from the binding of the two mol wt forms of IGF-II to receptors on rat placental membranes by the LIGAND program was consistent with a model in which 7.5K and 15K IGF-II bound to one site with Kd values of 0.27 +/- 0.03 and 0.38 +/- 0.04, respectively. There was an indication that 15K IGF-II also bound to a second low affinity site on the membrane. In mitogenesis assays performed on human fibroblasts isolated from the skin of two fetuses of an early gestational age, 15K IGF-II stimulated the incorporation of [3H]thymidine into DNA at a half-maximal concentration, i.e. ED50, of 5.7 and 5.0 nM. In these experiments, the ED50 values for 7.5K IGF-II were 8.7 and 15 nM.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism; D002845:Chromatography; D004247:DNA / Q000096:biosynthesis; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007335:Insulin-Like Growth Factor II / Q000302:isolation & purification* / Q000378:metabolism / Q000494:pharmacology; D008970:Molecular Weight; D010446:Peptide Fragments; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000302:isolation & purification*
D000596:Amino Acids; D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D010446:Peptide Fragments; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II; D004247:DNA; D011972:Receptor, Insulin