BLOOD-COAGULATION PROTEINS AND UROLITHIASIS ARE LINKED - CRYSTAL MATRIX PROTEIN IS THE F1 ACTIVATION PEPTIDE OF HUMAN PROTHROMBIN

Objectives To determine the relationship between prothrombin and crystal matrix protein (CMP), CMP is the predominant protein found in the organic matrix of calcium oxalate (CaOx) crystals generated from human urine and is a 31 kDa glycoprotein, whose N-terminal amino acid sequence shares homology with human prothrombin. Materials and methods CaOx crystallization was induced in ultrafiltered (UF) human urine containing either plasma or serum derived from the same healthy donor, by the addition of sodium oxalate. The crystals were demineralized and the resulting protein extracts analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting, using antibodies raised against human prothrombin and the C-terminus of prothrombin fragment 1+2 (F1+2). Results Prothrombin was detected in extracts of crystals precipitated from the UF urine in the presence of plasma, while CMP was completely absent, Crystals precipitated from UF urine supplemented with serum contained relatively large amounts of F1+2 and a protein with the same electrophoretic mobility as CMP. Analysis of a standard preparation of F1+2 which also contained prothrombin fragment 1 (F1) as a minor contaminant, showed a protein with electrophoretic and staining properties comparable to CMP. Conclusion CMP is a urinary form of F1, a degradation product of prothrombin possessing the domain rich in gamma-carboxyglutamic acid, which may have undergone some molecular modification either before or after its release into the urine.