Conformationally unstable antithrombin mutants. (A) 6 μmol/L WT and London (Δ393) antithrombin purified from plasma were incubated at 37 °C and 42°C for 3 d. Proteins were separated by nondenaturing electrophoresis and identified by western blot. Polymers were generated by heating WT antithrombin 10 min at 60°C. (B) Intracellular disulfide-linked polymers produced by constitutively conformational unstable recombinant antithrombin mutants. Intracellular lysate from cells transfected with WT plasmid was also run as a control. Disulfide-linked polymers were detected by SDS under nonreducing (SDS-nr) and reducing (SDS-r) conditions and Western blot.