title: Biochemical and biophysical characterization of photosystem I from phytoene desaturase and zeta-carotene desaturase deletion mutants of Synechocystis Sp. PCC 6803: evidence for PsaA- and PsaB-side electron transport in cyanobacteria.
abstract: In photosystem I, oxidation of reduced acceptor A(1)(-) through iron-sulfur cluster F(X) is biphasic with half-times of approximately 5-30 ns ("fast" phase) and approximately 150-300 ns ("slow" phase). Whether these biphasic kinetics reflect unidirectional electron transfer, involving only the PsaA-side phylloquinone or bi-directional electron transfer, involving both the PsaA- and PsaB-side phylloquinones, has been the source of some controversy. Brettel (Brettel, K. (1988) FEBS Lett. 239, 93-98) and Joliot and Joliot (Joliot, P., and Joliot, A. (1999) Biochemistry 38, 11130-11136) have attributed to nearby carotenoids electrochromic band shifts, accompanying A(1) reduction, centered at approximately 450 and 500-510 nm. As a test of these assignments, we separately deleted in Synechocystis sp. PCC 6803 the genes that encode phytoene desaturase (encoded by crtP (pds)) and zeta-carotene desaturase (encoded by crtQ (zds)). The pds(-) and zds(-) strains synthesize phytoene and zeta-carotene, respectively, both of which absorb to shorter wavelength than beta-carotene. Compared with wild type, the mutant A(1)(-) (FeS) - A(1)(FeS)(-) difference spectra, measured in cells and photosystem I complexes, retain the electrochromic band shift centered at 450 nm but show a complete loss of the electrochromic band shifts centered at 500-510 nm. Thus, the latter clearly arise from beta-carotene. In the wild type, the electrochromic band shift of the slow phase (centered at 500 nm) is shifted by 6 nm to the blue compared with the fast phase (centered at 506 nm). Thus, the carotenoid pigments acting as electrochromic markers during the fast and slow phases of A(1)(-) oxidation are different, indicating the involvement of both the PsaA- and the PsaB-side phylloquinones in photosystem I electron transport.
authors.affiliation: Central Research and Development, Experimental Station, E. I. du Pont de Nemours & Co., Wilmington, Delaware 19880-0173, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Bautista
authors.forename: Fabrice
authors.initials: F
authors.lastname: Rappaport
authors.forename: Mariana
authors.initials: M
authors.lastname: Guergova-Kuras
authors.forename: Rachel O
authors.initials: RO
authors.lastname: Cohen
authors.forename: John H
authors.initials: JH
authors.lastname: Golbeck
authors.forename: Jamie Yehong
authors.initials: JY
authors.lastname: Wang
authors.forename: Daniel
authors.initials: D
authors.lastname: Béal
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Diner
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D055592:Biophysical Phenomena; D001703:Biophysics; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D017353:Gene Deletion; D005798:Genes, Bacterial; D007700:Kinetics; D008958:Models, Molecular; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics*; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D013053:Spectrophotometry; D046939:Synechocystis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; C089909:photosystem I, psaB subunit; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; C099215:zeta-carotene desaturase