PARENT SESSION
Posters P1A Proton coupled electron transport and ATPase. Abstracts (172-180)

A novel oxidoreductase in the antimycin sensitive Photosystem I cyclic electron flow pathway (Synechocystis PCC6803). Hans Matthijs^*,1, Nataliya Yeremenko^*,1, Peerada Prommeenate², Wolfgang Schiefer³, Robert Jeanjean⁴, Peter Nixon^{2, 5}, Michel Havaux^*,5, ¹ Aquatic Microbiology, University of Amsterdam, Amsterdam, the Netherlands² Dept. Biol. Sciences, Imperial College London, London, United Kingdom³ Lehrstuhl Biochemie der Pflanzen, Bochum, Germany⁴ LCB-CNRS, , France, Marseille, France⁵ CEA/Cadarache, DSV, DEVM, Saint-Paul-lez-Durance, France

ABSTRACT- New results from gene array display prompted the design of a series of deletion mutants to clarify pathways and to evaluate the physiological significance of cyclic electron flow around Photosystem I in the cyanobacterium Synechocystis PCC 6803. Mutant characterization showed that products of the ORFs slr1208 and ssr 2016 (both till present known to encode so-called hypothetical proteins) were involved in cyclic electron flow in cyanobacteria and participate independently from the established constitutive NADH-dehydrogenase I, succinate dehydrogenease and the inducible ferredoxin:NADP⁺ mediated pathways. Both the slr1208 and ssr2016 knock-out mutants exhibited an antimycin A insensitive phenotype in Photosystem I (PS1) cyclic flow. This suggested the involvement of the gene products in the still poorly documented ferredoxin:quinone reductase mediated pathway. We studied a whole set of different knockout mutants with lesser pathways available and arrived at the conclusion that PSI cyclic electron flow attributed about 10% to the growth rate of cells incubated at optimal light intensity, and that the function of cyclic flow became more important at low light, with 20 to 30% reduction of the growth rate in the absence of PS1 cyclic flow and similar up to 70% at high light conditions. Mechanism and function of Photosystem I cyclic electron flow will be reviewed.

KEY WORDS: hypothetical proteins, redox, high and low light adaptation, Photosystem I cyclic electron flow, ferredoxin:quinone reductase and antimycin A