Purification and biochemical characterization of human liver-derived inhibitory protein (LIP).

The liver-derived inhibitory protein (LIP), described by us in 1974 (1), has now been purified and biochemically characterized. LIP was purified 166-fold from liver extract (LE) by a combination of gel filtration and ion exchange chromatography, using AcA 44, DEAE-cellulose, hydroxylapatite and Sephadex G-150 superfine. The m.w. of purified LIP was determined by gel filtration to be 67,000 daltons and by SDS-PAGE to be 37,000 daltons. The pI was in the range of 8.83 to 8.96. The protein is temperature labile (60 to 70 degrees C) and acid labile (pH 4). The specific lymphocyte inhibitory activity of the purified protein is 0.15 microgram/culture. LIP is distinct from other liver-derived inhibitory proteins.