Summary
Blood coagulation factor IX (Christmas factor) is a plasma protein which is required
for normal haemostasis. A functional deficiency of factor IX results in haemophilia
B, a bleeding disorder which is generally treated by infusions of factor IX concentrates
prepared from pooled human plasma. The use of human blood products is connected with
the risk of transmitting viral agents responsible for diseases such as hepatitis B
and AIDS. Recombinant DNA techniques may provide the means to produce the required
proteins without exposing the patients to these risks and at lower costs. One of the
problems which has to be overcome before recombinant factor IX can be used for therapeutical
purposes is related to the vitamin K-dependent carboxylation of its 12 NH2-terminal glutamate residues. In cell cultures this carboxylation, which is required
to render the protein its procoagulant activity, is far from complete, especially
at high expression levels. In this paper we describe the in vitro carboxylation of
non and/or partly carboxylated recombinant factor IX produced by transformed Chinese
hamster ovary cells. The identity of the newly formed Gla residues was verified and
it could be demonstrated that all carboxyl groups had been incorporated into the recombinant
factor IX.
Keywords
Vitamin K - Carboxylase - Haemophilia B - Factor IX
