Factors determining the special redox properties of photosynthetic cytochrome b559

摘要: Factors controlling the redox properties of two conventional forms cytochrome b559, i.e. unstable high-potential form and stable low-potential form, have been further investigated using PSII-enriched membranes from pea spinach chloroplasts. The potential b559 is pH independent both above 7.5 (E'm approximately +110 mV) below 6.0 +203 mV), but it changes with a slope 58 mV per unit between these values. Thus, seems to single ionizing group influencing its potential, higher affinity for protons in reduced (pK(red) = 7.5) lower oxidized (pK(ox) 6.0); consequently, one unprotonated (LP) protonated intermediate-potential (IP). (HP) pH-independent 5.0 8.0, relative content (compared total amount protein) decreases progressively 7.0. This conversion LP interpreted as corresponding loss proton by group, protonation which essential maintaining HP state. According chemical modification experiments diethylpyrocarbonate, histidine ligands heme be responsible existence IP forms. It proposed that difference due formation an additional hydrogen bond protein state stabilizes special hydrophobic environment high potential.