Abstract
Peptides from the venom ducts of cone snails (genus Conus) contain γ-carboxyglutamate residues. The γ-glutamyl carboxylase responsible for this post-translational modification is localized in the microsomal fraction, strictly dependent on vitamin K, activated by ammonium sulfate, and is associated with endogenous substrate. The K m of the enzyme for vitamin K is comparable to that for the bovine carboxylase. However, a propeptide containing substrate related to the blood coagulation protein factor IX, a highly efficient substrate for the bovine enzyme, was poorly carboxylated by the Conus enzyme, suggesting differences in γ-carboxylase recognition signal sequences and/or structural requirements at the carboxylation site.
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