| Autor: |
Francis, G. L., McNamara, P. J., Filsell, O. H., Ballard, F. J. |
| Zdroj: |
Journal of Endocrinology; May 1988, Vol. 117 Issue: 2 p183-189, 7p |
| Abstrakt: |
The clearance of labelled insulin-like growth factor-I (IGF-I) has been measured in lambs following acid gel-permeation chromatography and immunoprecipitation of plasma samples. The half-lives obtained in three experiments were between 5 and 7 h. Chromatography at neutral pH on a Fractogel HW55(S) column demonstrated that all the radioactivity associated with undegraded peptide in plasma was bound to a carrier protein. Similar studies with IGF-I that had been reduced by prior dithiothreitol treatment showed that two-thirds of the initial radioactivity in plasma decayed with a much shorter half-life and represented material that did not bind to carrier proteins in plasma. The remaining radioactivity was both associated with a binding protein and exhibited the characteristically long half-life of the native growth factor. Analysis of plasma samples using reversed-phase chromatography demonstrated that the radioactive component with a long half-life was IGF-I while that with a short half-life had been reoxidized to an incorrect form of the growth factor. When reoxidation of reduced IGF-I was blocked by S-carboxymethylation before injection of the radioactive peptide into lambs, it remained unbound in plasma and had a 0·8–0·9 h half-life. We suggest that reduced IGF-I only associates with the binding protein upon oxidation and correct folding and that this association is necessary in order for IGF-I to have a relatively long half-life.J. Endocr.(1988) 117,183–189 |
| Databáze: |
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