Immunoreactive and receptor-active insulin-like growth factor-I (IGF-I) and IGF-binding protein in blood plasma from the freshwater fish Macquaria ambigua (golden perch).
The presence of insulin-like growth factor-I (IGF-I)-related molecules and IGF-binding factors in blood from golden perch, Macquaria ambigua, an Australian native freshwater fish, was investigated. Serum was acidified to dissociate IGF and IGF-binding protein complexes that might be present, and fractionated by size-exclusion high-performance liquid chromatography at pH 2.8. Fractions were neutralized and their activities assessed by (i) an immunoassay for mammalian IGF-I which also detects chicken IGF-I but in which all known forms of IGF-II react very poorly, (ii) a receptor assay for IGF-II in which all known forms of IGF-I react poorly, and (iii) a type-I IGF receptor assay in which mammalian IGF-I and IGF-II polypeptides are amost equivalent. No IGF-II-like activity was detected. Three peaks of IGF-I-like activity were detected by IGF-I immunoassay and type-I IGF receptor assay. The major peak of activity was similar in molecular size to human IGF-binding protein-3, 45-55 kDa ('large IGF'), and a minor peak of activity which was similar in size to mammalian IGFs, 7.5 kDa. A third peak of activity was observed eluting at a time which indicates that it is a smaller molecule than any previously described IGF. The large IGF was temperature-sensitive, but was not a binding protein for 125I-labelled human IGF-I (hIGF-I). This material therefore was able to bind to anti-hIGF-I antibodies and to human type-I IGF receptors, and may represent the fish equivalent of mammalian prepro-IGFs.(ABSTRACT TRUNCATED AT 250 WORDS)
Anderson
T A
TA
Faculty of Aquatic Science, Deakin University, Geelong, Victoria, Australia.
Bennett
L R
LR
Conlon
M A
MA
Owens
P C
PC
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D007118:Immunoassay / Q000379:methods; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D010471:Perches / Q000097:blood*; D011863:Radioimmunoassay; D011869:Radioligand Assay; D013002:Somatomedins / Q000032:analysis*
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I