Calcium binding to the first EGF-like module of human factor IX in a recombinant fragment containing residues 1-85. Mutations V46E and Q50E each manifest a negligible increase in calcium affinity
The first EGF-like module of human coagulation factor IX contains a single functionally important calcium ion binding site. We have now shown the dissociation constant for this site to be approximately 160 microM in a recombinant protein fragment consisting of residues 1-85 in human fIX. This represents a approximately 10-fold increase in affinity as compared with the isolated EGF module (residues