Two different Ca2+ ion binding sites in factor VIIa and in des(1-38) factor VIIa.
The Ca2+ ion binding of factor VIIa and the derivative lacking the gamma-carboxyglutamic acid domain, des(1-38) factor VIIa, was investigated using intrinsic protein fluorescence and Tb3+ ion phosphorescence methods. Binding of Ca2+ ions giving rise to a decrease in the intrinsic protein fluorescence (approximately 50% at saturating conditions) is seen with both proteins. Each of the saturation curves is in accordance with the formation of a 1:1 complex of factor VIIa-Ca2+ (KD approximately 30 microM) and des(1-38) factor VIIa-Ca2+ (KD approximately 40 microM)). Yet another Ca2+ ion binding site reveals itself in each protein in Tb3+ ion phosphorescence experiments. Ca2+ ion competition studies have showed 1:1 complexes (KD's approximately 2 mM). The results are interpreted in terms of two different Ca2+ ion binding sites, one in the EGF-1 domain and one in the Gly-209-Gln-221 loop of the serine proteinase part.
Schiødt
J
J
Novo Nordisk Research Institute, Novo Nordisk A/S, Bagsvaerd, Denmark.
Harrit
N
N
Christensen
U
U
Petersen
L C
LC
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D015942:Factor VIIa / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013725:Terbium / Q000378:metabolism
D010446:Peptide Fragments; C075846:des(1-38) factor VIIa; D013725:Terbium; D015942:Factor VIIa; D002118:Calcium