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Two different Ca 2+ ion binding sites in factor VIIa and in des(1–38) factor VIIa
Author(s) -
Schiødt Jakob,
Harrit Niels,
Christensen Ulla,
Petersen Lars C.
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)81014-d
Subject(s) - chemistry , fluorescence , ion , binding site , c2 domain , biophysics , biochemistry , physics , organic chemistry , quantum mechanics , biology , membrane
The Ca 2+ ion binding of factor VIIa and the derivative lacking the γ‐carboxyglutamic acid domain, des(1–38) factor VIIa, was investigated using intrinsic protein fluorescence and Tb 3+ ion phosphorescence methods. Binding of Ca 2+ 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‐Ca 2+ ( K D ∼30 μM) and des(1–38) factor VIIa‐Ca 2+ ( K D ∼40 μM)). Yet another Ca 2+ ion binding site reveals itself in each protein in Tb 3+ ion phosphorescence experiments. Ca 2+ ion competition studies have showed 1:1 complexes ( K D ′s∼2 mM). The results are interpreted in terms of two different Ca 2+ ion binding sites, one in the EGF‐1 domain and one in the Gly‐209‐Gin‐221 loop of the serine proteinase part.