DETERGENT EFFECT ON CYTOCHROME b559 ELECTRON PARAMAGNETIC RESONANCE SIGNALS IN THE PHOTOSYSTEM II REACTION CENTRE. Yruela,

Detergent effect on Cytochrome b559 from spinach photosystem II was studied by electron paramagnetic resonance (EPR) spectroscopy in D1-D2-Cyt b559 complex preparations. Various n-dodecyl-β-D-maltoside concentrations from 0 to 0.2% (w/v) were used to stabilise the D1-D2-Cyt b559 complexes. Low spin heme EPR spectra were obtained but gz feature positions changed depending on detergent conditions. Redox potentiometric titrations showed a unique redox potential cytochrome b559 form (E ‘m = +123-150 mV) in all the D1-D2-Cyt b559 complex preparations indicating that detergent does not affect this property of the protein in those conditions. Similar effect on Cytochrome b559 EPR spectrum was observed in more intact photosystem II preparations independently of their aggregation state. This finding indicates that changes due to detergent could be a common phenomenon in photosystem II complexes. Results are discussed in terms of the environment each detergent provides to the protein.