Summary
Platelet factor 3 activity has been examined in the high (d,1.120) and low (d,1.090)
density platelet membranes obtained by the glycerol-lysis technique, and in the lipid
fractions extracted from them. The following observations were made : procoagulant
activity, as determined by the thromboplastin generation test, was equal in the two
types of membrane and was higher than in the intracellular fractions ; the lipid fraction
extracted from the low density membranes had a higher activity than that from the
high density membranes; at high concentrations this extracted phospholipid had a mild
anticoagulant effect. These results demonstrate functional differences between the
two types of platelet membrane and favor a plasma membrane origin for platelet factor
3.
