Binding of iron by factor IX. Possible role for beta-hydroxyaspartic acid.
In concentrations exceeding 1 mg/ml, bovine factor IX exhibits a pink color that arises from a broad absorption band with a lambda max = 500 nm. Analysis by x-ray fluorescence reveals the presence of iron but no other transition metals in the factor IX preparation. Quantitative analysis by atomic absorption spectroscopy indicates that 1 g atom of iron is bound tightly to 1 mol of factor IX. The iron is removed slowly (t1/2 = 3 h) by EDTA. In contrast, prothrombin binds no detectable iron, and factor X binds less than 0.2 g atom/mol. alpha-Hydroxybutyrate chelates Fe3+ with sufficient stability to preclude formation of [Fe(OH)3]n. It is proposed that factor IX binds iron with physiologically significant affinity and that the beta-hydroxyaspartate residue in factor IX is a chelator for the bound metal.
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives; D001665:Binding Sites; D002417:Cattle; D005164:Factor IX / Q000378:metabolism*; D005170:Factor X / Q000378:metabolism; D007501:Iron / Q000097:blood*; D007700:Kinetics; D011485:Protein Binding; D011516:Prothrombin / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
C011274:3-hydroxyaspartic acid; D001224:Aspartic Acid; D011516:Prothrombin; D005164:Factor IX; D005170:Factor X; D007501:Iron