Properties of glycosylated and non-glycosylated human recombinant IGF binding protein-3 (IGFBP-3).

The interaction of insulin-like growth factor-I with glycosylated and nonglycosylated human recombinant IGFBP-3 was studied by competition binding and by realtime biospecific interaction analysis (BIA). No significant difference was found in the affinity of the two forms of recombinant IGFBP-3 for IGF-I. Combining the results from the two different methods of binding analysis, a dissociation constant of 50 +/- 14 pM was determined. This value compares favorably to that reported for IGF-I binding to natural human plasma-derived IGFBP-3. Subcutaneous injection into rats of IGF-I either bound to glycosylated or nonglycosylated IGFBP-3 yielded an area under the curve (AUC) that was essentially the same for either form of IGFBP-3 and was twice as large as the AUC obtained after injection of IGF-I in the free form. Circulating IGF-I peak levels were reached in less than 1 h post-injection for free IGF-I, 4 and 8 h post-injection for the nonglycosylated and glycosylated IGF-I/IGFBP-3 complexes respectively. Neutral gel filtration of rat serum samples 4 and 8 h post-injection revealed that the IGF-I delivered bound to the nonglycosylated IGFBP-3 circulated as a 40-50 kDa complex at the 4 h time point and as a 130-140 kD complex at the 8 h time point. IGF-I delivered as a complex with glycosylated IGFBP-3 was found to circulate as a 140 kD complex at 4 and 8 h post-injection.(ABSTRACT TRUNCATED AT 250 WORDS)