polyP accelerates FXI autoactivation and FXIa autolysis. (A) Progress curves of FXI autoactivation in which 60nM FXI was incubated with 4μM polyP 77mer (○), 4μM polyP 255mer (●), or 2 μg/mL dextran sulfate (■). (B) PolyP polymer length dependence of the enhancement of FXI autoactivation. Second-order rate constants for FXI autoactivation (k2) were determined in reactions containing 30nM FXI and 4μM polyP of the indicated polymer lengths (0 indicates the absence of polyP). (C) SDS-PAGE analyses of FXI autoactivation in the presence of polyP (77mer or 225mer) or DS. Parallel timed samples from the experiment in panel B were resolved on reducing SDS-PAGE and silver stained. The position of FXI (Z) and the FXIa heavy chain (HC) and light chain (LC) are indicated. The lane labeled FXIa contained purified FXIa. (D) PolyP polymer length dependence of the enhancement of FXIa autolysis. Initial rates of loss of FXIa enzymatic activity were quantified in reactions containing 6nM FXIa and polyP preparations of varying polymer lengths, whose concentrations were adjusted to yield 3nM polymer (0 indicates the absence of polyP). Data in panels A, B, and D are mean ± SE (n = 3).
