Guinto E R, Esmon C T
J Biol Chem. 1982 Sep 10;257(17):10038-43.
Calcium binding to the activated form of blood coagulation Factor V (Factor Va) has been studied by equilibrium dialysis. A single calcium-binding site was observed with a dissociation constant of 24 +/- 4.0 microM. Unlike Factor V, Factor Va consists of two subunits. Following separation and reconstitution of the isolated subunits, a single calcium-binding site with a similar dissociation constant (24 +/- 2.0 microM) was again observed. No calcium binding was detected to either isolated subunit of Factor Va. Recombination of the Factor Va subunits used in the above equilibrium binding studies resulted in reformation of the calcium-binding site. Gel filtration experiments indicated that occupancy of this site with Ca2+ was required to maintain high affinity association between the Factor Va subunits. These data indicate that the calcium-binding site is either formed or stabilized by subunit-subunit interaction and that occupancy of this single site is sufficient to stabilize the intersubunit interactions.
通过平衡透析研究了钙与血液凝固因子V（因子Va）的活化形式的结合。观察到一个单一的钙结合位点，其解离常数为24±4.0微摩尔。与因子V不同，因子Va由两个亚基组成。分离并重组分离的亚基后，再次观察到一个具有相似解离常数（24±2.0微摩尔）的单一钙结合位点。未检测到钙与因子Va的任何一个分离亚基结合。上述平衡结合研究中使用的因子Va亚基的重组导致钙结合位点的重新形成。凝胶过滤实验表明，Ca2+占据该位点是维持因子Va亚基之间高亲和力结合所必需的。这些数据表明，钙结合位点是由亚基-亚基相互作用形成或稳定的，并且占据这个单一的位点足以稳定亚基间的相互作用。
