J. Biol. Chem., Vol. 261, Issue 11, 4833-4839, Apr, 1986
The effect of divalent metal ions on the electrophoretic mobility of bovine prothrombin and bovine prothrombin fragment 1
DW Deerfield 2d, P Berkowitz, DL Olson, S Wells, RA Hoke, KA Koehler, LG Pedersen and RG Hiskey
Examination of metal ion-dependent effects on the electrophoretic mobility
of bovine prothrombin and fragment 1 provides a useful and sensitive method
for investigation of conformational processes in these proteins.
Utilization of this method reveals a conformational change in bovine
prothrombin and fragment 1 which occurs at low metal ion concentrations.
Equilibrium dialysis studies indicate that the metal ion-induced shape
change occurs concomitant with binding of a single calcium ion/molecule of
prothrombin or fragment 1. Mixed metal electrophoretic mobility studies
with Mg2+ and Ca2+ have demonstrated the "synergistic" effect for fragment
1 observed by others. Mixed metal equilibrium dialysis has provided
experimental support for this observation and allows us to conclude that
two tight Ca2+ sites are not affected by low Mg2+ concentrations and that
the third Ca2+ site is also a tight site for Mg2+. Thus, at low Mg2+
concentrations and upon the addition of Ca2+, there are effectively three
tight sites; consequently more Ca2+ will bind to the protein at lower total
Ca2+ ion concentrations.
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