title: Stoichiometry of binding of high molecular weight kininogen to factor XI/XIa.
abstract: Factor XI is a dimeric protein and circulates in plasma complexed with high molecular weight kininogen (HMWK). We investigated the binding of HMWK to factor XIa utilizing two active site directed fluorescent probes: nitrobenzoxadiazole aminopentyl methylphosphonofluoridate for serine and dansyl-glu-gly-arg-chloromethyl ketone for histidine. In the presence of saturating amounts of HMWK, the fluorescence of factor XIa-fluorophore was quenched by approximately 28% for each probe. Titrations of the fluorescent factor XIa with HMWK revealed that each subunit of factor XIa binds one molecule of HMWK with a Kd approximately 3.4 X 10(-8)M.
mesh_terms: D001665:Binding Sites; D005172:Factor XI / Q000378:metabolism*; D015945:Factor XIa; D005456:Fluorescent Dyes; D006639:Histidine / Q000097:blood; D006801:Humans; D007704:Kininogens / Q000097:blood*; D008970:Molecular Weight; D011485:Protein Binding; D012694:Serine / Q000097:blood; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D007704:Kininogens; D012694:Serine; D006639:Histidine; D005172:Factor XI; D015945:Factor XIa