The effects of pH and Ca2+ on the intrinsic fluorescence of bovine prothrombin fragment 1 were investigated to deduce the nature of protein functional groups involved in Ca2+ binding to fragment 1. From pH values of 9 to 3, increasing the H3O+ concentration results in quenching of the fluorescence of fragment 1. Reversible pH-titration curves are obtained which appear to consist of two regions. From pH 4 to pH6.5 a broad titration curve is obtained, whereas from pH6.5 to 9 a more pronounced titration behaviour is evidenced by a group or groups on fragment 1 with an apparent pKa of approx. 7.5. In contrast, the apparent association constant for Ca2+ and fragment 1 shows a sharp pH-dependence in the region between pH7 and 8 with tighter Ca2+ binding at higher pH values. A PKa of approx. 7.5 can be estimated for the group or groups on fragment 1 linked to the tight binding of Ca2+. Both H3O+ and Ca2+ result in blue-shifts in the wave-lengths of fragment-1 emission. These results are interpreted in terms of H+ - and Ca2+ - induced changes in the conformation of fragment 1 as a result of surface-charge neutralization.
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Research Article| March 01 1979
The effects of calcium ions and pH on bovine prothrombin fragment 1. Intrinsic fluroescence studies
Biochem J (1979) 177 (3): 879–886.
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M E Scott, K A Koehler, R G Hiskey; The effects of calcium ions and pH on bovine prothrombin fragment 1. Intrinsic fluroescence studies. Biochem J 1 March 1979; 177 (3): 879–886. doi: https://doi.org/10.1042/bj1770879
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