Spectroscopic Studies of Photosystem II in Chlorophyll d-Containing Acaryochloris marina

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• 作者：M. Reza Razeghifard ; Min Chen ; Joseph L. Hughes ; Joel Freeman ; Elmars Krausz ; and Tom Wydrzynski
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：August 23, 2005
• 年：2005
• 卷：44
• 期：33
• 页码：11178 - 11187
• 全文大小：130K
• 年卷期：v.44,no.33(August 23, 2005)
• ISSN：1520-4995

文摘

Photosystem II (PSII) electron transfer (ET) in the chlorophyll d-containing cyanobacteriumAcaryochloris marina (A. marina) was studied by time-resolved electron paramagnetic resonance (EPR)spectroscopy at room temperature, chlorophyll fluorescence, and low-temperature optical spectroscopy.To maximize the ability to measure PSII ET in the intact cells of this organism, growth conditions wereoptimized to provide the highest specific O₂ activity and the instrumental parameters for the EPRmeasurements of tyrosine Z (Y_Z) reduction were adjusted to give the best signal-to-noise over spectralresolution. Analysis of the Y_Z^· reduction kinetics revealed that ET to the oxygen-evolving complex onthe donor side of PSII in A. marina is indistinguishable from that in higher plants and other cyanobacteria.Likewise, the charge recombination kinetics between the first plastoquinone acceptor Q_A and the donorside of PSII monitored by the chlorophyll fluorescence decay on the seconds time scale are not significantlydifferent between A. marina and non-chlorophyll d organisms, while low-temperature optical absorptionspectroscopy identified the primary electron acceptor in A. marina as pheophytin a. The results indicatethat, if the PSII primary electron donor in A. marina is made up of chlorophyll d instead of chlorophylla, then there must be very different interactions with the protein environment to account for the ETproperties, which are similar to higher plants and other cyanobacteria. Nevertheless, the water oxidationmechanism in A. marina is kinetically unaltered.