Hydrogen Metabolism

Ben‐Amotz, Ami

doi:10.1007/978-3-642-67242-2_38

Photosynthesis II 1979

DOI: 10.1007/978-3-642-67242-2_38

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Hydrogen Metabolism

Ami Ben‐Amotz¹

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1984

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Cited by 2 publications

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“…Most ofthe recent work connected with anaerobic metabolism in algae has focused on the assimilation and formation of H2 (4,18). As pointed out by Klein et al (20), since H2 is only one of several end-products of fermentation in green algae, it is necessary to place the H2 production in the broader context of the fermentative metabolism in order to gain a deeper understanding of the mechanisms that account for its evolution.…”

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confidence: 99%

Fermentative Metabolism of Chlamydomonas reinhardtii

Gfeller¹,

Gibbs²

1984

Plant Physiol.

245

128

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The anaerobic starch breakdown into end-products in the green alg Chiamydomonas reinhardtii F-60 has been investigted in the dark and in the light. The effects of 343,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) on the fermentation in the light have also been investigted.Anaerobic starch breakdown rnte (13.1 ± 3.5 micromoles C per milligram chlorophyll per hour) is increased 2-fold by FCCP in the dark. Light (100 watts per square meter) decreases up to 4-fold the dark rate, an inhibition reversed by FCCP. Stimulation of starch breakdown by the proton ionophore FCCP points to a pH-controlled rate-limiting step in the dark, while inhibition by light, and its reversal by FCCP, indicates a control by energy charge in the light.In the dark, formate, acetate, and ethanol are formed in the ratios of 2.07:1.07:0.91, and account for roughly 100% of the C from the starch.H2 production is OA3 mole per mole glucose in the starch. Glycerol >-lactate, and CO2 have been detected in minor amounts.In the light, with DCMU and FCCP present, acetate is produced in a 1:1 ratio to formate, and H2 evolution is 2.13 moles per mole glucose. When FCCP only is present, acetate production is lower, and CO2 and H2 evolution is 1.60 and 4.73 moles per mole glucose, respectively.When DCMU alone is present, CO2 and H2 photoevolution is higher than in the dark. Without DCMU, CO2 and H2 evolution is about 100% higher than in its presence. In both conditions, acetate is not formed. In all conditions in the light, ethanol is a minor product. Formate production is least affected by light.The stoichiometry in the dark indicates that starch is degraded via the glycolytic pathway, and pyruvate is broken down into acetyl- (3,19,20,28).Classical glycolysis followed by subsequent metabolism of the pyruvate to the various end-products has been proposed to account for the anaerobic catabolism of starch or glucose in the green algae (17,19,27). Except for H2 evolution, the effect of light on fermentative carbon flow has received little attention. This is principally due to the problems involved with photosynthetic fixation of the CO2 that might be evolved fermentatively. The first to attempt to resolve this question were Klein and Betz (20) who reported that light had no effect on the rate of starch breakdown or the pattern of fermentation in Chlamydomonas moewusii. But they used extremely low levels of light (160 lux (2) made use of C. reinhardtii F-60, a mutant characterized by an incomplete photosynthetic carbon reduction pathway but an intact photosynthetic electron transport chain, to monitor 'true' CO2 and H2 evolution. To account for their results, they proposed an involvement between anaerobic carbohydrate metabolism and the photosynthetic electron transport chain, implying that carbohydrate degradation is entirely or partially localized in the chloroplast. The purpose of our study was to establish for the first time a complete fermentative balance in C. reinhardtii F-60 between...

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Fermentative Metabolism of Chlamydomonas reinhardtii

Gfeller¹,

Gibbs²

1984

Plant Physiol.

245

128

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“…C. mundana, 'Boron' strain, was obtained from the algal collection at Gottingen. A common growth medium was devised from earlier ones for these species [20,21] : 20 mM Tris, 3 mM K2HP04, 7 mM NH4C1, acetic acid to give 200 pM CaC12 . 2 € 1 2 0 , 220 pM NaZEDTA, 100 pM FeS04.…”

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Interchangeable Copper and Iron Proteins in Algal Photosynthesis. Studies on Plastocyanin and Cytochrome c-552 in Chlamydomonas

1978

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The interrelation of the copper plastocyanin, and a soluble c‐type cytochrome, c‐552, in photosynthetic electron transport has been studies in the genus Chlamydomonas. With C. reinhardtii the plastocyanin:cytochrome c‐552 ration could be changes from 300:1 to < 1:16 simply by omitting copper from the medium, without any other detectable change. Plastocyanin was indetectable in a second species, C. mundana, for which the cytochrom c‐552 level was always very high. The properties of Levin's C. reinhardtii mutant lacking plastocyanin, ac‐208, were studies and it was foiund that the photosynthetic capabilities of a suppressed phenotype and suppressed genotype could be explained by reference to the cytochrome c‐552n levels. Both proteins were successfully used in reconsitution experiments with chloroplast fragments. Both showed very fast kinetics for reduction by purified Chlamydomonas cytochrome f, but the rate of electron transfer from one to other was much slower. It is concluded that they consitute an interchangeable pari, and the rationale for this and possible analogies are both discussed.

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Hydrogen Metabolism

Cited by 2 publications

References 69 publications

Fermentative Metabolism of Chlamydomonas reinhardtii

Fermentative Metabolism of Chlamydomonas reinhardtii

Interchangeable Copper and Iron Proteins in Algal Photosynthesis. Studies on Plastocyanin and Cytochrome c-552 in Chlamydomonas

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