The electron paramagnetic resonance spectra of partially purified cytochrome b6f complex from spinach

In addition to the signals exhibited by cytochrome f and a Rieske-type iron-sulfur cluster, cytochrome b 6 f preparations exhibit a broad asymmetric peak near g ∼ 3.7 due to cytochrome- b-563 components and a free radical signal which may be a bound semiquinone. Signals near g ∼ 6 and g ∼ 2.9 correspond at least in part to denatured cytochrome b-563; this suggests the possibility of strained bis-histine ligation in the native cytochrome. UHDBT but not antimycin A has a strong specific effect on the spectra of the complex.