title: Circular dichroism of the peripheral chlorophylls in photosystem II reaction centers revealed by electrochemical oxidation.
abstract: Visible absorption spectra and circular dichroism (CD) of the red absorption band of isolated photosystem II reaction centers were measured at room temperature during progressive bleaching by electrochemical oxidation, in comparison with aerobic photochemical destruction, and with anaerobic photooxidation in the presence of the artificial electron acceptor silicomolybdate. Initially, selective bleaching of peripheral chlorophylls absorbing at 672 nm was obtained by electrochemical oxidation at +0.9 V, whereas little selectivity was observed at higher potentials. Illumination in the presence of silicomolybdate did not cause a bleaching but a spectral broadening of the 672-nm band was observed, apparently in response to the oxidation of carotene. The 672-nm absorption band is shown to exhibit a positive CD, which accounts for the 674-nm shoulder in CD spectra at low temperature. The origin of this CD is discussed in view of the observation that all CD disappears with the 680-nm absorption band during aerobic photodestruction.
authors.affiliation: Chemistry Department, Udmurt State University, Universitetskaya 1, Izhevsk 426037, Russia. krop@uni.udm.ru
authors.forename: Tatyana N
authors.initials: TN
authors.lastname: Kropacheva
authors.forename: Marta
authors.initials: M
authors.lastname: Germano
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Zucchelli
authors.forename: Robert C
authors.initials: RC
authors.lastname: Jennings
authors.forename: Hans J
authors.initials: HJ
authors.lastname: van Gorkom
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D002942:Circular Dichroism; D003624:Darkness; D004563:Electrochemistry; D008982:Molybdenum / Q000737:chemistry; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011199:Potentiometry; D017655:Silicon Compounds / Q000737:chemistry
chemical_list: D045332:Photosystem II Protein Complex; D017655:Silicon Compounds; C013250:silicomolybdate; D002734:Chlorophyll; D008982:Molybdenum