Abstract
γ-carboxylated polypeptides were detected in the human kidney by immunohistochemistry with a monoclonal antibody (M3B) specific for γ-carboxyglutamyl residues. An ∼70-kDa γ-carboxylated protein, subsequently identified as prothrombin, was isolated from the intracellular compartment of cultured human embryonic kidney (HEK293) cells by immunoaffinity chromatography on M3B-coupled resin. Immunohistochemical analyses demonstrated that prothrombin and another vitamin K-dependent protein, the growth arrest-specific protein 6, were detectable in human kidney. As in the liver, the kidney synthesizes prothrombin as a zymogen that can be cleaved by ecarin to an amidolytically active serine protease that is inhibited by hirudin. This demonstrates for the first time the de novo synthesis of a full-length, γ-carboxylated, and functional prothrombin gene product by human kidney cells.
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