. "Edited: D'Eustachio, P, 0000-00-00 00:00:00"^^ . "Authored: D'Eustachio, P, 2005-01-20 14:44:36"^^ . "Factor XIa, bound to platelet glycoprotein (GP) Ib:IX:V on the platelet cell surface, catalyzes the formation of activated factor IX with high efficiency in a reaction that requires Ca++. The amino terminal part of the heavy chain of factor IX, the factor IX activation peptide, is released. (This peptide has no known function.)"^^ . . . . . . . "activation of factor IX (factor XIa catalyst)"^^ . "factor IX -> factor IXa + factor IX activation peptide (factor XIa catalyst)"^^ . "3.4.21"^^ . . . .