THE URINARY F1 ACTIVATION PEPTIDE OF HUMAN PROTHROMBIN IS A POTENT INHIBITOR OF CALCIUM-OXALATE CRYSTALLIZATION IN UNDILUTED HUMAN URINE IN-VITRO

1. The urinary F1 activation peptide of prothrombin is the predominant protein incorporated into calcium oxalate crystals precipitated from human urine. The aim of this study was to examine the effect of pure u rinary prothrombin F1 on calcium oxalate crystallization in human urin e. 2. Urinary prothrombin F1 was purified from demineralized calcium o xalate crystals precipitated from human urine, and its effects on calc ium oxalate crystallization induced by addition of an oxalate load wer e tested in undiluted, ultrafiltered urine from healthy men, at final concentrations of 0 to 10 mg/l. 3. Urinary prothrombin F1 did not affe ct the amount of oxalate required to induce crystallization, but the v olume of material deposited increased in proportion to increasing conc entrations of urinary prothrombin F1. However, the mean particle size decreased in reverse order: this was confirmed by scanning electron mi croscopy, which showed it to be the result of a reduction in crystal a ggregation rather than in the size of individual crystals. Analysis of C-14-oxalate data revealed a dose-dependent decrease in calcium oxala te deposition with an increase in urinary prothrombin F1 concentration , indicating that the increase in particle volume recorded by the Coul ter Counter resulted from inclusion of urinary prothrombin F1 into the crystalline architecture, rather than increased deposition of calcium oxalate. 4. It was concluded that urinary prothrombin F1 may be an im portant macromolecular determinant of stone formation.