pH dependence of magnesium ion binding to prothrombin fragment 1 and gamma-carboxyglutamic acid-containing peptides via 25Mg NMR.

The binding of magnesium ions to two tripeptides, $\text{L}$-Arg-$\text{D}$-Gla-$\text{D}$-Gla-OMe and Z-$\text{L}$-Arg(NO₂)-$\text{D}$-Gla-$\text{D}$-Gla-OMe, and to bovine prothrombin fragment 1 as a function of pH has been monitored by ²⁵Mg NMR spectroscopy. Binding to the tripeptide was dependent on peptide ionizations occurring at pH 4.6 – 4.8. The pH dependence of magnesium ion binding to fragment 1 reveals two inflection points 4.2 may be attributed to the deprotonation of the third side chain carboxylic acid group of the double γ-carboxyglutamic acid sequence. The origin of the increased binding of magnesium ions to fragment 1 at pH values above 7 is unknown.