['The homologous coagulation factor X (FX), VII (FVII), IX (FIX) and protein C (PC) display striking differences in the carboxyl-terminus, with that of FX being the most extended. This region is essential for FVII, FIX and PC secretion.', 'To provide experimental evidence for the role of the FX carboxyl-terminus.', 'Recombinant FX (rFX) variants were expressed in multiple eukaryotic cell systems. Protein and activity levels were evaluated by ELISA, coagulant and amidolytic assays.'] Is the carboxyl-terminal region essential for secreted and functional levels of coagulation factor X?