Stimulation of vitamin K-dependent carboxylation by pyridoxal-5′-phosphate

This paper presents evidence that the approximately two-fold increase in vitamin K-dependent carboxylation of the pentapeptide PheLeuGluGluLeu, but not of endogenous protein substrate, brought about by pyridoxal-5′-phosphate, is due to binding of the pyridoxal-5′-phosphate to microsomal enzyme(s), rather than to the pentapeptide. Pyridoxine inhibits this peptide carboxylation, while pyridoxal, pyridoxamine, and pyridoxamine-5′-phosphate have no effect on the reaction.