Calcium ion binding to human and bovine factor X.
Human and bovine factor X contain 11 and 12 glutamyl residues, respectively, within the first 40 amino terminal residues that are post-translationally modified to gamma-carboxyglutamyl (Gla) residues. We have measured calcium ion binding to human factor X by equilibrium dialysis. This is the first examination of calcium ion binding to human factor X. We have also re-examined the equilibrium dialysis binding of calcium ions to bovine facor X in order to compare the two species. The data was analysed using a variety of models that allow for more than one class of binding site and for co-operativity among binding sites. Calcium ion binding to human factor X fits a model that had two classes of sites: one class with a single site that had an affinity of 0.1 mM and a second class with 19 equivalent, non-interacting sites with an average affinity of 3.5 mM. There was no evidence for co-operativity in calcium ion binding. Calcium ion binding to bovine factor X was best stimulated by a model that assumed one tight site, four co-operative sites, and 18 equivalent, non-interacting sites. To examine the co-operativity seen in calcium ion binding to bovine factor X, calcium ion binding to isolated Gla region (residues 1-44) and Gla-domainless factor X was measured by equilibrium dialysis. Calcium ion binding to Gla-domainless factor X was simulated by a model that had two classes of sites: one class with a single site that had an affinity of 0.25 mM, and a second class that had 15 sites with very low affinity sites (greater than 15 mM).(ABSTRACT TRUNCATED AT 250 WORDS)
Monroe
D M
DM
Department of Hematology, University of North Carolina, Chapel Hill 27599-7035.
Deerfield
D W
DW
Olson
D L
DL
Stewart
T N
TN
Treanor
R E
RE
Roberts
H R
HR
Hiskey
R G
RG
Pedersen
L G
LG
D015055:1-Carboxyglutamic Acid; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle / Q000097:blood*; D003956:Dialysis; D005170:Factor X / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011516:Prothrombin / Q000378:metabolism; D013045:Species Specificity
D015055:1-Carboxyglutamic Acid; D011516:Prothrombin; D005170:Factor X; D002118:Calcium