Fragments of bovine insulin-like growth factors I and II stimulate proliferation of rat L6 myoblast cells.
The active sites of bovine insulin-like growth factor (IGF) I and II fragments were studied. Overlapping fragments of IGF I (residues 1-25, 11-35, 21-45, 31-55, and 41-70) and of IGF II (residues 1-24, 10-34, 20-44, 30-54, and 40-67) were chemically synthesized. The activity of the fragments was measured by stimulating the proliferation of rat L6 myoblast cells. Two fragments of IGF I (residues 21-45 and 31-55) and two fragments of IGF II (residues 20-44 and 30-54) were active while the other fragments were inactive in stimulating cell proliferation. Although the activity of these fragments was observed only at a high concentration of 0.1 mM, the results imply that the active site is located around residues 31-45 for IGF I fragments and residues 30-44 for IGF II fragments. Consequently, an IGF I fragment (residues 26-50) having a five-residue extension to both the N- and C-terminal sites of residues 31-45 also stimulated the proliferation of L6 myoblast cells. Furthermore, the substitution of Ile-35 in two IGF II fragments (residues 21-45 and 31-55) by Ser inactivated these fragments. This suggests that Ile-35 is an essential residue for IGF II fragment activity. Ser-35, which was reported in the original sequencing of bovine IGF II, is incorrect in the sequence and furthermore has been consistently found to be an Ile-35 in our hands.(ABSTRACT TRUNCATED AT 250 WORDS)
Konishi
Y
Y
Monsanto Company, St. Louis, Missouri 63198.
Kotts
C E
CE
Bullock
L D
LD
Tou
J S
JS
Johnson
D A
DA
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002455:Cell Division; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis / Q000302:isolation & purification / Q000502:physiology*; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis / Q000302:isolation & purification / Q000502:physiology*; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012995:Solubility; D013002:Somatomedins / Q000502:physiology*
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II