Fraction G from Cerastes vipera venom previously purified on Sephadex
G100 was refractionated on DEAE-Sephadex A50 column. A factor X activa
tor was obtained. It had a mol. wt of 12,500 and an isoelectric point
of 4.4. It shortened the plasma recalcification time of normal plasma,
and plasmas deficient in factors V, VII, VIII, IX, XI and XIII, while
it had no effect on plasma deficient in factor X or factor II. It had
a serine protease activity and a minimal plasmin activity. PMSF, leup
eptin and iodoacetamide exerted a pronounced inhibitory effect on its
serine protease activity. Polyantivenin could neutralize the coagulant
activity of the activator.