Purification and Characterization of Tumor Invasion‐inhibiting Factors

Tumor invasion‐inhibiting factors were purified from bovine liver using an in vitro system for estimating the tumor invasion ability. The acid‐ethanol extract of liver was subjected to ultrafiltration (Amicon PM10 membrane), and the fraction corresponding to the molecular weight range below 10,000 was further fractionated by ion‐exchange (DEAE‐Toyopearl), gel filtration (Bio‐Gel P6), and reverse‐phase (C18) chromatographies. Two types of active polypeptides with molecular weights of about 5,000 and 2,000 were purified and named IIF‐1 and IIF‐2, respectively. Both peptides inhibited tumor invasion with half‐maximum concentrations of 2–6 ng/ml in vitro. The amino acid compositions of both peptides were determined.