| Popis: |
Insulin-like growth factor-I (IGF-I) is one of the most abundant growth factors in circulation (~200 ng/ml); however, very little of it exists in its free form. Normally, IGF-I is bound to one of its six known binding proteins designated as IGFBPs1–6 (1, 2). These IGFBPs exhibit variable tissue distributions and are believed to be involved in modulation of IGF activity (3–7). In circulation, IGF-I exists primarily as part of a ternary complex comprised of equimolar ratios of IGF-I, IGFBP-3, and a protein known as acid labile subunit (ALS) (1, 8). IGFBP-3 is by far the most abundant IGF binding protein and the only form that can bind to ALS to form the large 150-kd ternary complex. This complex found in serum greatly extends the circulating time of IGF-I and is believed to modulate the availability of free IGF-I (1, 9). |
