MONOMERIC FERRIC HEME PEPTIDE DERIVATIVES - MODEL SYSTEMS FOR HEMOPROTEINS

Electron paramagnetic resonance spectra of a number of ferric heme pep tide derivatives, in aqueous-detergent and various aqueous-alcohol sol vent mixtures, have been obtained using samples in the concentration r ange 0.1-1.0 mM. Some of these were clearly monomeric, homogeneous, mi xed-ligand adducts, entirely suitable for use as model systems for hem oprotein specroscopic studies. As anticipated, the measured EPR parame ters were largely independent of solvent environment. Surprisingly, mi cellar preparations of ferric heme undecapeptide in mildly alkaline so lution showed no evidence for the formation of a hydroxide adduct, con trary to a previous report [S. Mazumdar, O. K. Medhi and S. Mitra, Ino rg. Chem. 30 700 (1991)].