Vitamin K dependent carboxylation: synthesis and biological properties of tetrazolyl analogues of pentapeptidic substrates.

The pentapeptides Phe-Leu-X-Glu-Val and Phe-Leu-X-X-Val, where X = 4-(5H-tetrazolyl)-2-aminobutyric acid (tetrazolyl analogue of glutamic acid), were synthesized by addition of tri-n-butyltin azide to the corresponding nitrile-containing peptides. These tetrazolyl peptides and a dinitrile precursor were tested as possible substrates and inhibitors of the vitamin K dependent carboxylation. Phe-Leu-X-Glu-Val was carboxylated (40% of the reference peptide Phe-Leu-Glu-Glu-Val, Km = 20 mM) exclusively on the glutamyl residue, whereas the dinitrile precursor and Phe-Leu-X-X-Val were not carboxylated. The latter was a competitive inhibitor with an affinity (Ki = 3 mM) close to that of the reference peptide (Km = 3 mM).