FIGURE 2.

Relative rates of S-2765 hydrolysis by bovine factor X_a (5 nM) as a function of C6PS in the presence of 5 mM Ca²⁺ (filled circles), 2 mM Ca²⁺ (filled triangles), and in the absence of Ca²⁺ (filled squares) were determined at 37°C in a buffer containing 50mM Tris, 175 mM NaCl, 0.6% PEG, at pH 7.6. The data are expressed as a fraction of the rate of S2765 hydrolysis by factor X_a in the absence of C6PS. The lines indicate the fits of the data to a model assuming a single C6PS site on factor X_a, yielding dissociation constants of 190 and 98 μM in the presence of 2 and 5 mM Ca²⁺, respectively.