Plastoquinonesareeffectivelyreducedbyferredoxin:NADP + oxidoreductaseinthepresenceofsodiumcholatemicelles Significanceforcyclicelectrontransportandchlororespiration MonikaBojko,JerzyKruk*,Stanis awWic ˛ c eckowski Department of Physiology and Biochemistry of Plants, Faculty of Biotechnology, Jagiellonian University, ul. Gronostajowa 7, 30-387 Krako ´w, Poland Received28April2003;receivedinrevisedform28July2003 Abstract The effect of sodium cholate and other detergents (Triton X-100, sodium dodecyl sulphate, octyl glucoside, myristyl- trimethylammoniumbromide)onthereductionofplastoquinones(PQ)withadifferentlengthoftheside-chainbyspinachferre- doxin:NADP + oxidoreductase(FNR)inthepresenceofNADPHhasbeenstudied.BothNADPHoxidationandoxygenuptake duetoplastosemiquinoneautoxidationwerehighlystimulatedonlyinthepresenceofsodiumcholateamongtheuseddetergents. Sodiumcholateattheconcentrationof20mMwasfoundtobethemosteffectiveonbothPQ-4andPQ-9-mediatedoxygenuptake. TheFNR-dependentreductionofplastoquinonesincorporatedintosodiumcholatemicelleswasstimulatedbyspinachferredoxin but inhibited by Mg 2+ ions. It was concluded that the structure of sodium cholate micelles facilitates contact of plastoquinone moleculeswiththeenzymeandcreatesfavourableconditionsforthereactionsimilartothosefoundinthylakoidmembranesfor PQ-9reduction.TheobtainedresultswerediscussedintermsofthefunctionofFNRasaferredoxin:plastoquinonereductaseboth incyclicelectrontransportandchlororespiration. # 2003ElsevierLtd.Allrightsreserved. Keywords: Ferredoxin-NADP + oxidoreductase;Plastoquinone;Chlororespiration;Sodiumcholate;Micelles 1. Introduction Ferredoxin:NADP + oxidoreductase (EC 1.18.1.2) catalyzes reduction of NADP + in stroma of chloro- plasts and this reaction is the last step of the linear photosynthetic electron transport chain (for review see Arakakietal.,1997).However,theroleofFNRinthe cyclic electron transport around photosystem I and chlororespiration has not been elucidated (Moss and Bendall, 1984; Hosler and Yocum, 1985; Bendall and Manasse, 1995; Arakaki et al., 1997; Wic ˛ c eckowski and Bojko, 1997; Hoefnagel et al., 1988; Peltier and Cour- nac, 2002).Ithasbeensuggestedthatthereductionof plastoquinone pool is catalyzed by a NAD(P)H dehy- drogenase [NAD(P)H:plastoquinone reductase] (Gue- deneyetal.,1995,1996;Endoetal.,1997;Corneilleet al.,1998),cytochrome b 6 –f complex(Clarketal.,1984; Zhangetal.,2001),cytochrome b 559 ofphotosystemII (KrukandStrzaka,1999)FNR(Bo¨hme,1977;Shahak, 1981) or by a hypothetical ferredoxin : plastoquinone reductase(FQR)(MossandBendall,1984;Bendalland Manasse,1995;Endoetal.,1997).Theresultsobtained previously by our group indicate that FNR may be engagedinthisprocess.Wehavefoundthattheisolated FNR is able to reduce directly many prenylquinones (Bojko and Wic ˛ c eckowski, 1999) and that the quinone- bindingsiteattheenzymemoleculecorrespondstothe DCPIP-binding site and this site differs from those involved in ferredoxin oxidation or NADP + reduction (Changetal.,1991;BojkoandWic ˛ c eckowski,2001).The isolatedFNRwasshowntoreduceeffectivelyshort-chain 0031-9422/$-seefrontmatter # 2003ElsevierLtd.Allrightsreserved. doi:10.1016/S0031-9422(03)00506-5 Phytochemistry64(2003)1055–1060 www.elsevier.com/locate/phytochem Abbreviations: ApoFd,apoferredoxin;FNR,ferredoxin:NADP + oxidoreductase; Fd, ferredoxin; FQR, ferredoxin:plastoquinone reductase; PQ, plastoquinone; NADP + , b-nicotinamide adenine di- nucleotide phosphate; CMC, critical micelle concentration; CHAPS, 3[(3-cholamidopropyl) dimethylammonio]-1-propane sulphonate; MTAB, myristyltrimethylammonium bromide; OG, octyl glucoside; SDS, sodium dodecylsulphate; DCPIP, 2,6-dichloro- phenolindophenol. * Corresponding author. Tel. +48-12-252-6361; fax: +48-12-633- 6907. E-mail address: jkruk@mol.uj.edu.pl(J.Kruk).