SDS-PAGE and Coomassie (or silver) stain of unbound and eluted proteins, from β2GPI affinity column, derived from different platelet membrane preparations. (A) Proteins from HD1 platelet preparation; MW indicates molecular weight marker; lane 1, complete platelet lysate; lane 2, platelet membrane protein extract; lane 3, unbound proteins; lane 4, eluted proteins (39 kDa and approximately 8 kDa). (B) Proteins from HD2 platelet preparation; MW indicates molecular weight marker; lane 1, unbound proteins; lane 2, eluted proteins (30 kDa and approximately 9 kDa). (C) Proteins from HD3 platelet preparation; MW indicates molecular weight marker; lane 1, unbound proteins; lane 2, eluted proteins (40 kDa, 30 kDa, 19 kDa, 15 kDa, 8 kDa). (D) Proteins from platelet preparations from patients with APS; MW indicates molecular weight marker; lanes 1 to 7, single eluted protein (8 kDa) from patients with APS 1 to 7. (E) MS/MS analysis of the 8-kDa protein eluted from β2GPI affinity column. Generated fragments of precursor ion m/z 761.35 correspond to the peptide AGPHCPTAQLIATLK. Experimentally detected y- and b-ions are marked in bold (color).