Enzymatic degradation of the factor-VIII-von-Willebrand protein: a unique tryptic fragment with ristocetin cofactor activity

Humanvon Willebrand protein was purified from pooled cryoprecipitate, then degraded by trypsin and analyzed primarily for ristocetin cofactor activity in relation to the electrophoretic pattern in sodium dodecyl sulfate polyacrylamide gradient gels.Activity decreased rapidly at first.from 55 to 5.5 U/mI of activity after 20 mm of degradation.in association with the appearance and disappearance of fragments of molecular weight equal to or greater than 314.000.Ristocetin cofactor activity remained constant at 1 .7-3.6 U/mI during the remainder of the 90-mm hydrolysis.The contribution of individual degradation products to this residual activity of the digest.which contained more than twice the activity in normal human plasma.was assessed by gel filtration of 30.45. and 90-mm digests through Sephacryl 5-200 columns.Activity paralleled the second protein peak.which eluted at 1 .31void volume.Sodium dodecyl sulfate-polyacrylamide gradient gel analysis of