Human Platelet - Derived Mitogens . I . Identification of Insulinlike Growth Factors I and II by Purification and N # { 176 } Amino Acid Sequence Analysis

Human platelet lysates contained potent mitogenic activities for MCF-7 human breast-cancer cells in serum-freedefined media. Because these activities were not replaced by known platelet mitogens. such as platelet-derived growth factor or transforming growth factor , we sought to identify the breast cancer cell mitogens by purification and N amino-acid sequencing. Acetic acid extracts of outdated human platelets were concentrated by ammonium sulfate precipitation and fractionated on Sephadex G-50 and Bio-Gel P-b columns in 0.5 mol/L acetic acid. Two major activities were resolved by molecular sieve methods and fractionated further by reverse-phase highperformance liquid chromatography (HPLC). Purifications (70.000 to 870.000-fold) were accomplished yielding mol