CHARACTERIZATION OF ZINC-SUBSTITUTED CYCTOCHROME-C BY CIRCULAR-DICHROISM AND RESONANCE RAMAN-SPECTROSCOPIC METHODS

Iron(III) in cytochrome c is replaced with zinc(II) by a modification of a method published by others, and the procedure is described in ful l detail. Three forms of cytochrome c-those containing iron(III), iron (II), and zinc(II)-are examined by circular dichroism spectroscopy and resonance Raman spectroscopy. Spectra of both kinds show that introdu ction of zinc(II) ions does not appreciably alter the overall structur e and conformation of cytochrome c. Resonance Raman spectra indicate t he size of the porphyrin ''core'' that is inconsistent with six-coordi nation and consistent with five-coordination. Unlike the iron(III) and iron(II) ions, which are bound to two axial ligands (His 18 and Met 8 0), the zinc(II) ion in cytochrome c seems to be bound to only one, mo st probably His 18. Evidence pertaining to the question of axial coord ination is discussed. (C) 1997 Elsevier Science Inc.