REACTIONS OF MONOPEROXOVANADATE AND DIPEROXOVANADATES WITH PEPTIDES CONTAINING FUNCTIONALIZED SIDE-CHAINS

The equilibria established between the mono- and diperoxovanadates and a number of di- and tripeptides in aqueous solution has been studied by V-51 NMR spectroscopy. Both monoperoxovanadate and diperoxovanadate react favorably with a number of these peptido ligands. However, the mode of complexation is quite different for the two types of peroxovanadates. Diperoxovanadate gives rise to unidentate products with condensation occurring through the carboxyl or amino groups and also through the aromatic hydroxyl of tyrosyl residues. Particularly favored complexes are formed with imidazole nitrogens, but complexes that involved tryptophan nitrogens were not observed to form. In contrast with diperoxovanadate, monoperoxovanadate forms multidentate complexes with the peptides studied. These materials form slowly but are highly favored. For the simple dipeptide, glycylglycine, the amino group, the carboxyl group, and the peptide nitrogen comprise the points of attachment. The carboxylate group can be replaced by a hydroxymethyl as in glycylserine. Also, the peptide nitrogen, but apparently not the carboxyl or amino groups, can be substituted by a histidine imidazole nitrogen. Tryptophan nitrogens, as similarly found for diperoxovanadates, do not appear to undergo significant interactions with monoperoxovanadate. Although phenol and tyrosyl hydroxyl groups undergo moderately strong interactions with monoperoxovanadate, no corresponding monodentate reactions were observed with imidazole rings. Some possible biochemical implications of this work are discussed.