Binding of Ca 2+ to normal and dicoumarol-induced prothrombin

The Ca²⁺ binding properties of normal bovine prothrombin have been studied and compared with those of an abnormal bovine prothrombin induced by dicoumarol. The normal prothrombin binds up to 10–12 Ca²⁺ per mole of protein. The three first Ca²⁺ were bound to sites which exhibited positive cooperativity. A Ca²⁺ dependent conformational change was demonstrated during the binding of the first three Ca²⁺. In contrast with normal prothrombin, the dicoumarol-induced prothrombin had only one high affinity binding site. No ligand-induced conformational change was detected in this prothrombin.