title: The influence of sodium ion binding on factor IXa activity.
abstract: Sodium plays an important role in modulating both the amidolytic and proteolytic activities of thrombin. By contrast, while the optimal amidolytic activity of factor Xa requires Na(+), the proteolytic activity of factor Xa in the prothrombinase complex is minimally affected by the monovalent cation. In this study, we analyzed the effect of Na(+) on the amidolytic and proteolytic activity of factor IXa in the absence and presence of factor VIIIa. Factor IXa exhibited normal activity towards a fIXa-specific chromogenic substrate and antithrombin in the presence of physiological concentrations of Ca(2+) with no obvious requirement for Na(+) in either reaction. Further studies revealed that factor IXa binds to its cofactor factor VIIIa with a normal affinity in the absence of Na(+) and that the catalytic function in the intrinsic Xase complex is also independent of Na(+) in the presence of physiological concentrations of Ca(2+). These results suggest that unlike the important role that Na(+) plays in modulating the macromolecular substrate specificity of thrombin, the monovalent cation is not required for the physiological function of factor Ixa in the intrinsic Xase complex.
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, 1402 S. Grand Blvd., MO 63104, USA.
authors.forename: Kota
authors.initials: K
authors.lastname: Gopalakrishna
authors.forename: Alireza R
authors.initials: AR
authors.lastname: Rezaie
mesh_terms: D000494:Allosteric Regulation; D000991:Antithrombins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D001779:Blood Coagulation Factors / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002863:Chromogenic Compounds; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D015949:Factor IXa / Q000737:chemistry* / Q000378:metabolism; D015944:Factor VIIIa / Q000737:chemistry / Q000378:metabolism; D005170:Factor X / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism; D009842:Oligopeptides; D011485:Protein Binding; D012964:Sodium / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000991:Antithrombins; D001779:Blood Coagulation Factors; D002863:Chromogenic Compounds; D009363:Neoplasm Proteins; D009842:Oligopeptides; D015944:Factor VIIIa; C035205:methylsulfonylleucyl-glycyl-arginine-4-nitroanilide; D005170:Factor X; D012964:Sodium; D015949:Factor IXa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant; D002118:Calcium