Decreased inhibitory activity of prothrombin to calcium oxalate crystallization by specific chemical modification of its gamma-carboxyglutamic acid residues

Objectives. To investigate the inhibitory role of gamma (gamma)-carboxyglutamic acid (Gla) in the Gla domain of urinary prothrombin in the formation of calcium oxalate crystals. Methods. Morpholine and formaldehyde at different concentrations were added to the solution of prothrombin to cause the conversion of Gla to gamma-methyleneglutamic acid (MGlu). The extent of the modification was controlled by the relative amount of modification reagents to prothrombin. The 100-fold molar excess of modification reagents to prothrombin produced the prothrombin molecule containing 2 gamma-MGlu residues, and the 10,000-fold molar excess produced the molecule containing 8 gamma-MClu residues. The inhibitory activities of prothrombin and modified prothrombin to calcium oxalate crystallization were evaluated by the seeded crystallization technique. Results. The inhibitory index of Gla prothrombin to calcium oxalate crystallization was 14.2%, that of 2 gamma-MGlu prothrombin was 12.8%, decreased by about 10%, and that of 8 gamma-MGlu prothrombin was 5.0%, decreased by about 65%. Conclusions. The Gla in the Gla domain of urinary prothrombin may play an important role in inhibiting the formation of renal calcium oxalate calculus.