SDS-PAGE of plasma-derived ¹²⁵I-X and recombinant ¹²⁵I-X in 15% polyacrylamide gels. Plasma-derived ¹²⁵I-X (lanes 1 and 3) and recombinant¹²⁵I-X (lanes 2 and 4) were subjected to 15% SDS-PAGE and autoradiography, under nonreducing conditions (lanes 1 and 2) and reducing conditions (lanes 3 and 4) (68-kD single chain; 47-kD heavy chain; 23-kD light chain).