The Effect of Bicarbonate on Photosynthetic Oxygen Evolution in Flashing Light in Chloroplast Fragments

Stemler, Alan; Babcock, Gerald T.

doi:10.1073/pnas.71.12.4679

Cited by 30 publications

(19 citation statements)

References 11 publications

(14 reference statements)

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“…(3) Addition of chemical analogs of BC, such as formate (Stemler and Radmer 1975) or acetate (Stemler et al 1974) (see Scheme 1) is thought to replace BC from its binding site(s) in PSII (Method 3). In this study we carefully monitor the inorganic carbon levels in the buffers during sample incubation and under measurement conditions by membrane-inlet mass spectrometry (MIMS).…”

Section: Introductionmentioning

confidence: 99%

Interactions of photosystem II with bicarbonate, formate and acetate

Shevela¹,

Klimov

Messinger³

2007

Photosynth Res

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In this study, we probe the effects of bicarbonate (hydrogencarbonate), BC, removal from photosystem II in spinach thylakoids by measuring flash-induced oxygen evolution patterns (FIOPs) with a Joliot-type electrode. For this we compared three commonly employed methods: (1) washing in BC-free medium, (2) formate addition, and (3) acetate addition. Washing of the samples with buffers depleted of BC and CO2 by bubbling with argon (Method 1) under our conditions leads to an increase in the double hit parameter of the first flash (beta 1), while the miss parameter and the overall activity remain unchanged. In contrast, addition of 40-50 mM formate or acetate results in a significant increase in the miss parameter and to an approximately 50% (formate) and approximately 10% (acetate) inhibition of the overall oxygen evolution activity, but not to an increased beta 1 parameter. All described effects could be reversed by washing with formate/acetate free buffer and/or addition of 2-10 mM bicarbonate. The redox potential of the water-oxidizing complex (WOC) in samples treated by Method 1 is compared to samples containing 2 mM bicarbonate in two ways: (1) The lifetimes of the S0, S2, and S3 states were measured, and no differences were found between the two sample types. (2) The S1, S0, S(-1), and S(-2) states were probed by incubation with small concentrations of NH2OH. These experiments displayed a subtle, yet highly reproducible difference in the apparent Si/S(-i) state distribution which is shown to arise from the interaction of BC with PSII in the already reduced states of the WOC. These data are discussed in detail by also taking into account the CO2 concentrations present in the buffers after argon bubbling and during the measurements. These values were measured by membrane-inlet mass spectrometry (MIMS).

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Section: Introductionmentioning

confidence: 99%

Interactions of photosystem II with bicarbonate, formate and acetate

Shevela¹,

Klimov

Messinger³

2007

Photosynth Res

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“…PSII of green algae, for example, is inhibited if bicarbonate is removed from the reaction mixture and substituted for by formate (Mende and Wiessner, 1985). Bicarbonate is also reported (1) to stabilize the OEC (for review, see Klimov and Baranov, 2001), (2) to promote the photoassembly of the Mn 4 Ca complex (for review, see Ananyev et al, 2001), and (3) to interfere with the damping of the oscillatory pattern of oxygen evolution (Stemler et al, 1974). Finally, in the currently most complete structural model of PSII at 3.5 Å resolution (Ferreira et al, 2004), (bi)carbonate is presented as a ligand of the Mn 4 Ca complex.…”

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Evidence That Bicarbonate Is Not the Substrate in Photosynthetic Oxygen Evolution

et al. 2005

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(J.C., W.J.); and Max-PlanckInstitut fü r Bioanorganische Chemie, 45470 Muelheim an der Ruhr, Germany (K.B., J.M.)It is widely accepted that the oxygen produced by photosystem II of cyanobacteria, algae, and plants is derived from water. Earlier proposals that bicarbonate may serve as substrate or catalytic intermediate are almost forgotten, though not rigorously disproved. These latter proposals imply that CO 2 is an intermediate product of oxygen production in addition to O 2 . In this work, we investigated this possible role of exchangeable HCO 3 2 in oxygen evolution in two independent ways. (1) We studied a possible product inhibition of the electron transfer into the catalytic Mn 4 Ca complex during the oxygen-evolving reaction by greatly increasing the pressure of CO 2 . This was monitored by absorption transients in the near UV. We found that a 3,000-fold increase of the CO 2 pressure over ambient conditions did not affect the UV transient, whereas the S 3 / S 4 / S 0 transition was half-inhibited by raising the O 2 pressure only 10-fold over ambient, as previously established. (2) The flash-induced O 2 and CO 2 production by photosystem II was followed simultaneously with membrane inlet mass spectrometry under approximately 15% H 2 18 O enrichment. Light flashes that revealed the known oscillatory O 2 release failed to produce any oscillatory CO 2 signal. Both types of results exclude that exchangeable bicarbonate is the substrate for (and CO 2 an intermediate product of) oxygen evolution by photosynthesis. The possibility that a tightly bound carbonate or bicarbonate is a cofactor of photosynthetic water oxidation has remained.

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“…

It is established that PSII activity in chloroplast membranes requires catalytic amounts of dissolved CO2 (11,12,15). This substance, denoted as C',2 is bound to the reaction center complex (9).

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Forms of Dissolved Carbon Dioxide Required for Photosystem II Activity in Chloroplast Membranes

Stemler

1980

Plant Physiol.

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It is established that PSII activity in chloroplast membranes requires catalytic amounts of dissolved CO2 (11,12,15). This substance, denoted as C',2 is bound to the reaction center complex (9). It has not been determined with certainty if CO2 or HCO3 is the active form. The ligand interacts with the reaction center in a dynamic fashion (10). It is released very briefly in light, possibly when electrons are passed from the reaction center to PC, but is bound again in a subsequent "dark" reaction. To understand this cyclic binding and release of the ligand and to formulate an explanation of the "bicarbonate effect," it is necessary to know the form of inorganic carbon which is taken up, used and released by the reaction center. Early experiments indicated that HCO3 was, in fact, the "active form" (3,6,12). This conclusion, however, remained tentative.A previous study (10) room temperature and harvested 8-14 days after planting. After harvesting, the leaves were ground for 30 s in a Waring Blendor set at maximum speed. This grinding regime will yield predominantly mesophyll grana but no attempt was made to completely exclude bundle sheath chloroplasts. The isolation medium contained 0.4 M sucrose, 0.01 M NaCi, and 0.05 M Na-phosphate (pH 6.8). All operations were done at near freezing temperatures. After grinding, the chloroplast slurry was filtered through four layers of cheesecloth and the filtrate was centrifuged for 1 min at 200g. The supernatant suspension was poured into clean tubes and centrifuged for 5 min at 1,500g. The resulting supernatant fluid was discarded. The chloroplasts comprising the pellet were then osmotically shocked by suspension in sucrose-free isolation medium. The broken chloroplasts were collected by centrifugation at 1,500g for 5 min. The resulting pellet was resuspended in a small amount of isolation medium, divided into portions, placed in a freezer and kept at -80 C. The chloroplasts were thawed just before use.To deplete chloroplasts of endogenous C', thawed grana were suspended in depletion medium which contained 0.175 M NaCl, 0.1 M sodium formate, and 0.05 M Na-phosphate (pH 5.0). TheChl concentration was about 50 jg/ml. The room-temperature suspension was allowed to stand for 10 min, then it was centrifuged. The thylakoid membranes, now depleted of C', were resuspended in a small amount of depletion medium and kept on ice until used (see ref. 9).Ferricyanide-supported 02 evolution was monitored with a Rank Brothers, Clark-type electrode. The light source was a Sylvania 150-w projector lamp and the light was focused by a Prado slide projector. The incident light intensity of white light was 500 w/m2.The rate of binding of radioactive C' to PSII reaction centers was measured as follows. Broken chloroplasts were depleted of endogenous C' by the procedure given above. They were then collected by centrifugation and resuspended in a small amount of depletion medium. In some experiments the chloroplasts were suspended in other media as noted in the figure legends. Twenty

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The Effect of Bicarbonate on Photosynthetic Oxygen Evolution in Flashing Light in Chloroplast Fragments

Cited by 30 publications

References 11 publications

Interactions of photosystem II with bicarbonate, formate and acetate

Interactions of photosystem II with bicarbonate, formate and acetate

Evidence That Bicarbonate Is Not the Substrate in Photosynthetic Oxygen Evolution

Forms of Dissolved Carbon Dioxide Required for Photosystem II Activity in Chloroplast Membranes

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