STABILIZATION OF HYDROLYTICALLY LABILE IRON(II)-CYSTEINE PEPTIDE THIOLATE COMPLEXES IN AQUEOUS TRITON X-100 MICELLE SOLUTION - SPECTROSCOPIC PROPERTIES MIMICKING OF REDUCED RUBREDOXIN

The absorption, CD, and H-1- and F-19-nmr spectroscopic features of Fe (II) complexes with a series of cysteine-containing oligopeptides were investigated in aqueous (H2O or D2O) 10% Triton X-100 micelle solutio n. The complexes with distal aromatic rings, [Fe(Z-cys-Pro-Leu-cys-Gly -X)(2)](2-) (Z = benzyloxycarbonyl; X = NH-C6H4-p-F, NH-CH2-CH2-C6H4-p -F, and Phe-OMe), were found to be quite stable in such aqueous micell e solution. The coordination of cysteine-peptide ligands to the Fe(II) ion is revealed by isotropically shifted H-1-nmr signals due to the C ys CbetaH2 protons occurring at 120 similar to 250 ppm in a D2O Triton X-100 micelle solution (10%) at 60 degrees C that are very similar to those reported for native reduced rubredoxin. The high stability of t hese cysteine peptide-Fe(II) complexes in aqueous micellar system was explained by the combined contributions from NH-S hydrogen bonds and t he effect of the proximity of aromatic groups. The existence of such N H-S hydrogen bonds and interactions between aromatic ring and sulfur a tom was confirmed by F-19-nmr spectral and F-19 spin-lattice relaxatio n times (T-1) measurements. (C) 1998 John Wiley & Sons, Inc.