title: Interactions of vitamin K-dependent proteins with calcium ions and phospholipid membranes.
abstract: The calcium-dependent interaction of vitamin K-dependent proteins with membranes is a complex process that minimally consists of 1) calcium binding to the protein and an essential calcium-dependent protein transition, 2) an essential calcium-membrane interaction, and 3) formation of the protein-membrane complex. Below about 5 mM calcium, the protein-membrane complex binds more calcium than the sum of the components but at higher concentrations protein-membrane binding is not accompanied by additional cation binding. These protein-menbrane interactions function in blood coagulation by increasing the binding affinity of the active site. The increased affinity results from the additive effects of protein-membrane (e.g., prothrombin-, factor Xa- and factor V-membrane) interactions and protein-protein (e.g., factor Xa- factor V and prothrombin-factor V) interactions. The prothrombinase complex can be viewed kinetically as a dissociable three-component enzyme (factor Xa, factor V, and phospholipid) acting on the soluble substrate, prothrombin.
mesh_terms: D001777:Blood Coagulation; D002118:Calcium / Q000378:metabolism*; D005165:Factor V / Q000378:metabolism; D005170:Factor X / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008566:Membranes / Q000378:metabolism*; D008954:Models, Biological; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D011516:Prothrombin / Q000378:metabolism; D013917:Thrombin / Q000096:biosynthesis; D014812:Vitamin K / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D010743:Phospholipids; D014812:Vitamin K; D005165:Factor V; D011516:Prothrombin; D005170:Factor X; D013917:Thrombin; D002118:Calcium