Antenna function of a chlorophyll ab protein complex of Photosystem I

Ortiz, William; Lam, Eric; Ghirardi, Maria L.; Malkin, Richard

doi:10.1016/0005-2728(84)90267-6

Cited by 38 publications

(15 citation statements)

References 14 publications

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“…[I] in having more Chl in the reaction centre (P700 Chl,-Pl) and less in the antennae. The nearly equal distribution of Chl between antennae and reaction centre agrees with the results of Ortiz et al [17].…”

Section: Methodssupporting

confidence: 82%

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Chlorophyll‐protein complexes of barley photosystem I

Bassi

Simpson

1987

European Journal of Biochemistry

205

142

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Photosystem I (PSI) preparations with a chlorophyll a/b ratio of 6.0 were isolated from barley thylakoids using two different methods. The high-molecular-mass complex (CPla*) which is resolved by non-denaturing gel electrophoresis had the same properties as a PSI preparation (PSI-200) isolated by Triton X-1 00 solubilisation of thylakoids followed by sucrose gradient ultracentrifugation. This material had a chlorophyll : P700 ratio of 208 : I and was composed of three different chlorophyll-protein complexes which could be separated from each other by solubilising the PSI preparation in dodecyl maltoside followed by sucrose gradient ultracentrifugation. Approximately half of the chlorophyll, including all the chlorophyll h, was located in two antenna complexes designated LHCI-680 and LHCI-730, which were identified by their characteristic low-temperature fluorescence emission spectra. The rest of the chlorophyll a was associated with the PSI reaction centre, P700 Ch1,-P1, which fluoresced at 720 nm. Each chlorophyll-protein complex had a unique polypeptide composition and characteristic circular dichroic and absorption spectra. The use of dodecyl maltoside instead of dodecyl sulphate resulted in a less denatured form of LHCI-680, which fluoresced at 690 nm at 77 K. One of the sucrose gradient fractions contained a complex consisting of only LHCI-730 and P700 Ch1,-P1 which fluoresced at 731 nm, indicating that LHCI-730 is structurally associated with P700 Chl,-P3 and quenches its fluorescence. Approximately threequarters of the light-harvesting antenna chlorophyll was in LHCI-730, but only about one-quarter of the normal complement of LHCI-730 was required to quench the reaction centre.By reducing the amount of Triton relative to the chlorophyll concentration, a PSI preparation (chlorophyll a/h ratio of 3.5) with a chlorophyll:P700 ratio of 300:l was isolated. It contained no photosystem 11, but a significant amount of LHCII which was functionally connected to the PSI reaction centre. Reconstitution studies demonstrated that excitation energy transfer from LHCII to PSI requires the presence of LHCI-680, and we propose that, in PSI, the following linear excitation energy transfer sequence occurs: LHCII + LHCI-680 4 LHCI-730 + P700 Chl,-Pl.Much of our present knowledge of the structure and composition of photosystem I (PSI) in higher plant thylakoids was made possible by the work of Mullet et al. [l] who isolated and characterised a functional PSI preparation in high yield from pea leaves. It retained the long-wavelength low-temperature fluorescence emission typical of whole thylakoids and supported electron transport from dichloroindophenol to methyl viologen. The existence of a PSI-specific lightharvesting chlorophyll-protein complex (LHCI) was predicted from the reduction in antenna size of a PSI 'core' preparation [l] Abbreviations. CD, circular dichroism; Chl, chlorophyll; LHC, light-harvesting chlorophyll protein; PAGE, polyacrylamide gel electrophoresis; PS, photosystem; SDS, sodium dodecyl sulphate. fluores...

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Section: Methodssupporting

confidence: 82%

“…Correction for the steadystate nature of the photochemical measurement gave a Chl:P700 ratio of 95, close to that calculated using the equations of Table 2. This is higher than the LHCI-depleted PSI preparation of Mullet et al (Chl:P700 of 65), but consistent with values for Synechococcus [16] and spinach [17].…”

Section: Methodsmentioning

confidence: 55%

Chlorophyll‐protein complexes of barley photosystem I

Bassi

Simpson

1987

European Journal of Biochemistry

205

142

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“…LHCI 730 shows an, absorption peak at a longer wavelength than LHCI 680 (676-677 nm vs 670-674 nm) and different CD spectra, confirming that they are distinct chlorophyll-proteins (Lam et al, 1984b;Bassi et al, 1985;Bassi and Simpson, 1987). Three and two polypeptides have been associated respectively to LHCI-730 and LHCI-680 in the MW range of 20-25 kDa (Lam et al, 1984;Bassi et al, 1985), while the earlier report of a 10 kDa component (Haworth et a/., 1983;Ortiz et al, 1985) was not confirmed in later studies (Lam et al, 1984a;Bassi et al, 1985;Machold, 1986;Bassi and Simpson, 1987). The two LHCI complexes differed in the extent they are exposed to the solvent: LHCI-730 was shown to be buried in the hydrophobic portion of the membrane, while LHCI-680 was surface exposed, based on proteolytic digestion and labeling with a chemical probe (Ortiz et al, 1985) or antibodies (Ryrie et al, 1985).…”

Section: Chlorophyll Alb Proteins Of Photosystem Imentioning

confidence: 86%

“…Photoprotection of RC I by thermal conversion has been proposed as the main LHCI function, since the appearance of 60 ps fluorescence emission from LHCI under closed trap conditions was only accompanied by a rise in fluorescence yield of a factor of 1.45, in agreement with the low probability for an anti-Stokes energy transfer for LHCI to RC I (Rubin and Paschenko, 1986). However, the antenna size of a PSI preparation including LHCI was found to be twice that of a PSI preparation without LHCI (Ortiz et al, 1984;Bassi and Simpson, 1987), suggesting that the whole LHCI complement transfers energy to RC I. To reconcile these results, an allosteric mechanism may be hypothesized, switching LHCI from a dissipative to a conservative state according to the redox state of PSI.…”

Section: Chlorophyll Alb Proteins Of Photosystem Imentioning

confidence: 99%

CHLOROPHYLL BINDING PROTEINS WITH ANTENNA FUNCTION IN HIGHER PLANTS and GREEN ALGAE

Bassi

Rigoni

Giacometti

1990

Photochem & Photobiology

158

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“…This procedure resulted in the isolation of a PSI complex which contained approximately 200 to 250 Chl/P700 and had a Chl a/b ratio of -5. These properties are similar to those for the complexes isolated from thylakoid membranes from higher plants, and these complexes have been shown by several groups to retain the in vivo organization and composition of Chl associated with PSI (5,22,25 In an attempt to define the role of some of these PSI subunits, the native PSI complex has been fractionated into an LHCP I antenna and a Chl a-containing PSI core complex (11,25), as described in "Materials and Methods." The core complex contains -125 Chl/P700 and retains photochemical activity while the antenna complex shows no photochemical activity.…”

mentioning

confidence: 99%