Proton, calcium, and magnesium binding by peptides containing gamma-carboxyglutamic acid.

gamma-Carboxyglutamic acid (Gla) is believed to bind Ca II] ions and Mg II] ions in prothrombin and other coagulation proteins. Binding constants for H+, Ca II] ions, and Mg II] ions to Gla-containing peptides are determined using pH and ion selective electrode titrations. The binding constants for peptides containing a single Gla residue are similar to the constants for malonic acid. Peptides containing two Gla residues in sequence (di-Gla peptides) bind Ca II] ions and Mg II] ions more strongly. KMgL for the di-Gla peptides is similar to the site-binding constant for Ca II] ions in denatured BF1. These di-Gla peptides may be useful analogs for metal binding by the disordered Gla domain in BF1.