Plasma aggregating factor (bovine) for human platelets: a marker for study of antihemophilic and von Willebrand Factors.

The human-platelet aggregating factor in preparations of bovine plasma and bovine antihemophilic factor has been reported to be an activity of bovine antihemophilic factor. However, we show that activities of aggregating factor and antihemophilic factor are present in varying proportion in different preparations of antihemophilic factor. Aggregating factor activity is more stable on storage than is antihemophilic factor activity and can be selectively adsorbed by human platelets. Further, antihemophilic factor activity free of aggregating activity was eluted from DEAE-Sephadex. The factors were also separated during agarose chromatography in 0.25 M CaCl(2), which yields a small-molecular-weight moiety with antihemophilic factor activity; aggregating factor activity continued to elute in the void volume. Thus, aggregating factor activity is clearly separable from antihemophilic factor activity. The usual physiologic platelet-aggregating reactions require fresh platelets. Fresh, aged, and sonicated platelets, but not platelets that have been frozen and thawed, react with aggregating factor, indicating that the platelet "receptor sites" for the aggregating factor are unusually stable.