Synthetic peptides including the γ-carboxylation recognition site and acidic amino acids were compared as substrates for vitamin K-dependent γ-carboxylation by bovine liver carboxylase. The 28-residue proPT28 (proprothrombin -18 to +10) and proFIX28 (proFactor IX -18 to +10) were carboxylated with a K(m) of 3 μM. The V(max) of proPT28 was 2-3 times greater than that of proFIX28. An analog of proFIX28 that contained the prothrombin propeptide had a V(max) 2-3-fold greater than an analog of proPT28 that contained the Factor IX propeptide.proFIX28/RS-1, based upon Factor IX Cambridge, proFIX28/RQ-4, based upon Factor IX Oxford 3, and proFIX28 had equivalent K(m) and V(max) values. Analogs of proPT28 containing Ala6-Glu7 or Glu6-Ala7 were carboxylated at equivalent rates. A peptide containing Asp6-Asp7 was carboxylated at a rate of about 1% of that of Glu carboxylation. Carboxylation of peptides containing Asp6-Glu7 and Glu6-Asp7 yielded results identical with peptides containing Ala6-Glu7 and Glu6-Ala7. Carboxymethylcysteine was not carboxylated when substituted for Glu6 in a peptide containing Asp7. These results indicate that the prothrombin propeptide is more efficient in the carboxylation process than is the Factor IX propeptide, but that both propetides direct carboxylation; the γ-carboxylation recognition site does not include residues -4 and -1; aspartic acid and carboxymethylcysteine are poor substrates for the carboxylase, but aspartic acid does not inhibit the carboxylation of adjacent glutamic acids.
|Number of pages||6|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 1 Jan 1989|