title: Trehalose stimulation of photoinduced electron transfer and oxygen photoconsumption in Mn-depleted photosystem 2 membrane fragments.
abstract: It is known that the removal of manganese from the water-oxidizing complex (WOC) of photosystem 2 (PS2) leads to activation of oxygen photoconsumption (OPC) [Khorobrykh et al., 2002; Yanykin et al., 2010] that is accompanied by the formation of organic hydroperoxides on the electron-donor side of PS2 [Khorobrykh et al., 2011]. In the present work the effect of trehalose on the OPC in Mn-depleted PS2 preparations (apo-WOC-PS2) was investigated. A more than two-fold increase of the OPC is revealed upon the addition of 1M trehalose. Drastic (30%-70%) inhibition of the OPC upon the addition of either electron acceptor or electron donor indicates that the trehalose-induced activation of the OPC occurs on both donor and acceptor sides of PS2. A two-fold increase in the rate of superoxide-anion radical photoproduction on the electron-acceptor side of PS2 was also shown. Applying the "variable" chlorophyll fluorescence (ΔF) it was shown that the addition of trehalose induces: (i) a significant increase in the ability of exogenous Mn(2+) to donate electrons to the reaction center of PS2, (ii) slowing down the photoaccumulation of the primary quinone electron acceptor of PS2 (QA(-)) under aerobic conditions, (iii) acceleration of the reoxidation of QA(-) by QB (and by QB(-)) as well as the replacement of QB(2-) by a fully oxidized plastoquinone, and (iv) restoration of the electron transfer between the quinone electron carriers in the so-called "closed reaction centers of PS2" (their content in the apo-WOC-PS2 is 41%). It is suggested that the trehalose-induced increase in efficiency of the O2 interaction with the electron-donor and electron-acceptor sides of apo-WOC-PS2 is due to structural changes leading to both a decrease in the proportion of the "closed PS2 reaction centers" and an increase in the electron transfer rate in PS2.
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Moscow Region, Russia. Electronic address: ya-d-ozh@rambler.ru.
authors.forename: D V
authors.initials: DV
authors.lastname: Yanykin
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Moscow Region, Russia.
authors.forename: A A
authors.initials: AA
authors.lastname: Khorobrykh
authors.affiliation: M. V. Lomonosov Moscow State University, A. N. Belozersky Institute of Physical-Chemical Biology, Moscow 119991, Russia.
authors.forename: M D
authors.initials: MD
authors.lastname: Mamedov
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Moscow Region, Russia.
authors.forename: V V
authors.initials: VV
authors.lastname: Klimov
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D008345:Manganese; D010100:Oxygen / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism*; D018724:Spinacia oleracea / Q000166:cytology; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D014199:Trehalose / Q000494:pharmacology*; D014867:Water / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D002734:Chlorophyll; D008345:Manganese; D014199:Trehalose; D010100:Oxygen
keywords: Electron transfer; Manganese; Oxygen photoconsumption; Photosystem 2; Superoxide anion-radical; Trehalose