Studies on the procoagulant activity of human amniotic fluid. I. Stability and coagulation factor requirements

A fraction of human amniotic fluid possessing procoagulant activity was purified 35-70 fold by gel filtration on Sepharose 4B. The activity eluted in the void volume indicating a particle size in excess of 5 X 10(6) daltons. The amniotic fluid factor (AFF) activity is stabilized on storage in the presence of Ca++ ions which could not be replaced by Mg++. Addition of phospholipids resulted in accelerated loss of activity. Steps taken to remove factor VII did not affect the activity, but factor X and V are required.