Iron-sulfur centers of the chloroplast membrane

EPR spectroscopy of semi-methemerythrin

EPR spectra of semi-met forms of octameric hemerythrin from Themiste zostericola, prepared by one electron reduction of methemerythrin or by one electron oxidation of deoxyhemerythrin, have been visualized at liquid helium temperatures. The spectrum of that prepared by one electron reduction has principal g-values of 1.96 +/- 0.01, 1.88 +/- 0.01, and 1.67 +/- 0.02 while that obtained by one electron oxidation has g = 1.95 +/- 0.01, 1.72 +/- 0.01, and 1.68 +/- 0.02. The amplitude of either spectrum decreases with time on incubation at room temperature according to a first order rate with t 1/2 = 5-8 min, apparently because of an intramolecular disproportionation. Similar EPR spectra have been obtained with semi-metmyohemerythrin of T. zostericola and with the octameric semi-met form of Phascolopsis gouldii. However, these forms disproportionate to a much lesser degree. The azide adduct of the octameric semi-met form of T. zostericola has g-values of 1.94 +/- 0.01, 1.85 +/- 0.01, and 1.57 +/- 0.02. Its EPR spectrum differs somewhat from those of the azide adducts of the octamer of P. gouldii and the monomer of T. zostericola although all are resistant to disproportionation. Methemerythrin and deoxyhemerythrin have no EPR spectra even at liquid helium temperature.