The nature of the interaction between ristocetin-Willebrand factor VIIi coagulant activity molecule

Brockway, W.J.; Fass, D.N.

Journal of Laboratory and Clinical Medicine 89(6): 1295-1305


ISSN/ISBN: 0022-2143
PMID: 16975
Accession: 068518035

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The association:dissociation reaction between porcine ristocetin-Willebrand factor (RWF) and porcine factor VIII coagulant activity molecule was studied with sucrose gradient centrifugation techniques. Internal markers were added to quantitate sedimentation coefficients. The S value of the factor VIII coagulant molecule was varied between 26 S and 10.5 S depending upon the concentration of NaCl added to the gradient. At low concentrations of NaCl (0.15-0.35 M), S values of 20-26 S were observed. At NaCl concentrations near 0.4 M, factor VIII coagulant was observed at both 25 S and 10.5 S. Between 0.55 M and 1.5 M NaCl, only 1 low S value peak of factor VIII coagulant (10.5 S) was observed. The S value of the RWF was essentially independent of the NaCl concentration (25-32 S). Porcine von Willebrand plasma contained only a low S value factor VIII coagulant (6.4-7.8 S) regardless of the NaCl concentration. When purified RWF was added to the von Willebrand plasma, a high S value factor VIII coagulant peak (22.5 S) was obtained. The addition to porcine plasma of a rabbit IgG preparation directed against purified RWF resulted in only the low S value (9.3 S) factor VIII coagulant peak being seen following centrifugation. CaCl2 also dissociated the factor VIII coagulant activity molecule. Even in the case of von Willebrand plasma, a peak of high S value (28.2 S) factor VIII coagulant activity was also found in the presence of greater than 0.025 M CaCl2. The effect of varying the pH between pH 6.0 and 8.5 indicated that dissociation of the 2 activities is favored at the lower pH. These results are consistent with the hypothesis that in vivo the factor VIII coagulant molecule and the RWF form a loose complex. Under certain conditions (NaCl, CaCl2, pH) these 2 molecules can be dissociated and upon dissociation can both still express their individual activities.