Biochemical and Biophysical Characterization of Photosystem I from Phytoene Desaturase and ζ-Carotene Desaturase Deletion Mutants of Synechocystis Sp. PCC 6803

Abstract

In photosystem I, oxidation of reduced acceptor A 1 ؊ through iron-sulfur cluster F X is biphasic with halftimes of ϳ5-30 ns ("fast" phase) and ϳ150 -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 ؊ 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 ␤-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.

Construction and Characterization of Genetically Modified Synechocystis sp. PCC 6803 Photosystem II Core Complexes Containing Carotenoids with Shorter π-Conjugation than β-Carotene

“…2A). This strain required glucose and dim light for growth and contained functional Photosystem I (PS I) but no PS II, as indicated by the absence of a variable chlorophyll fluorescence yield upon illumination of dark-adapted cells (27). Failure to isolate PS II core complexes using chromatographic methods also confirmed the absence of PS II centers in this strain.…”

“…We have learned what types of carotenoids can be incorporated into PS II. We have found that gene deletions that block ␤-carotene formation do not result in PS II formation (27). However, expressing phytoene desaturase from Rhodobacter capsulatus in Synechocystis in place of the endogenous -carotene and phytoene desaturases, results in the accumulation of carotenoids that can be incorporated into PS II.…”

Sll0254 (CrtL diox ) Is a Bifunctional Lycopene Cyclase/Dioxygenase in Cyanobacteria Producing Myxoxanthophyll

“…Cell pellets were frozen in liquid nitrogen and freeze-dried. Pigments were extracted from freeze-dried cells by three successive extractions with methanol that contained 0.1% NH 4 OH, and extracts were combined and evaporated under a stream of nitrogen until the samples were dry. Dried samples were redissolved in a small volume of NH 4 OH-containing methanol and immediately subjected to high-performance liquid chromatography (HPLC) on an HP-1100 Chemstation with a Waters Spherisorb S5ODS2 (4.0 mm by 250 mm) column filled with C-18 reversed phase silica gel, using a linear 18-min gradient of ethyl acetate (0 to 95%) in acetonitrile-water-triethylamine (9:1:0.01, vol/vol/ vol) at a flow rate of 1 ml/min.…”

Myxoxanthophyll Is Required for Normal Cell Wall Structure and Thylakoid Organization in the Cyanobacterium Synechocystis sp. Strain PCC 6803

“…6G). To discriminate between effects due to the absence of just fucose (important for cell wall structure [38,57]) and of myxoxanthophyll, ⌬slr0940K, a strain lacking -carotene desaturase (CrtQ) that is needed for carotenoid formation (5,8), was included in this study as well: differences between the wild type and ⌬sll1213Z that are due to myxoxanthophyll should be visible also in ⌬slr0940K, which lacks myxoxanthophyll, whereas features shared by the wild type and ⌬slr0940K but not by ⌬sll1213Z presumably involve just fucose. As shown in Fig.…”