IDENTIFICATION OF A VITAMIN-K-DEPENDENT CARBOXYLASE IN THE VENOM DUCTOF A CONUS SNAIL

Peptides from the venom ducts of cone snails (genus Coitus) contain ga mma-carboxyglutamate residues. The gamma-glutamyl carboxylase responsi ble for this post-translational modification is localized in the micro somal fraction, strictly dependent on vitamin It, activated by ammoniu m 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 coag ulation protein factor IX, a highly efficient substrate for the bovine enzyme, was poorly carboxylated by the Conus enzyme, suggesting diffe rences in gamma-carboxylase recognition signal sequences and/or struct ural requirements at the carboxylation site. (C) 1997 Federation of Eu ropean Biochemical Societies.