The Mechanism of Hydrogen Photoevolution in Photosynthetic Organisms

King, Dan; Erbes, David L.; Ben‐Amotz, Ami; Gibbs, Martin

doi:10.1016/b978-0-12-500650-7.50010-6

Cited by 8 publications

(2 citation statements)

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“…Under light conditions NADH should give its electrons by a lightdriven reaction through the electron transport chain of photosynthesis to hydrogenase. This idea ofa light-driven electron transport from HADH to hydrogenase has been supported by Ben-Amotz and Gibbs (1) and King et al (13), who assumed plastoquinone to be the site of NADH oxidation. A similar mechanism for the light-dependent evolution of H2 by Scenedesmus has been proposed by Kaltwasser et al (1 1), who also started to elucidate the fermentation of Scenedesmus.…”

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confidence: 53%

Fermentative Metabolism of Hydrogen-evolving Chlamydomonas moewusii

Klein

Betz²

1978

Plant Physiol.

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The anaerobic metabolism of Chiamydomonas moewusii under both light (160 lux) and dark conditions has been examined using manometric and enzymic techniques. During anaerobiosis starch is broken down to glycerol, acetate, ethanol, C02, and H2. The release of CO2 and H2 comes to an end when the starch pool is depleted. There are only slight differences in the ratio of the end products of fermentation between light and dark metabolism. In the light, glycerol production is diminished and H2 evolution is enhanced, whereas the production rate of all other end products generally does not change. Chlamydomonas moewusii belongs to a group of unicellular green algae which are capable of utilizing or evolving molecular hydrogen (6, 9, 14). The evolution of H2 arises in darkness or in light, if the cells are exposed to anaerobiosis in an atmosphere of N2 or inert gas. There have been several suggestions to explain this H2 evolution as part of the fermentative metabolism of green algae. In their first paper about H2 production in Scenedesmus Gaffron and Rubin (7) suggested that the evolution of H2 depends at least in the dark on the degradation of a reserve substance. Exogenous glucose, which was fermented to lactic acid, increased the rate of H2 evolution. Damaschke (5) got similar results with Chlorella pyrenoidosa, which also produced lactic acid during fermentation and which could be stimulated by glucose too. For Chlamydomonas Healey (9) proposed a fermentative process including the citric acid cycle as source for H2 evolution in the dark. He assumed that the surplus NADH could either reduce some unknown acceptor or bring its electrons to a higher redox level at the expense of ATP from where H2 would be released. Under light conditions NADH should give its electrons by a light-driven reaction through the electron transport chain of photosyn-thesis to hydrogenase. This idea ofa light-driven electron transport from HADH to hydrogenase has been supported by Ben-Amotz and Gibbs (1) and King et al. (13), who assumed plastoquinone to be the site of NADH oxidation. A similar mechanism for the light-dependent evolution of H2 by Scenedesmus has been proposed by Kaltwasser et al. (1 1), who also started to elucidate the fermentation of Scenedesmus. To evaluate the validity of all of these suggested mechanisms for the evolution of H2 it seems necessary to know first the anaerobic metabolism of green algae. This includes the measurement of substrates and end products of fermentation in algae. This paper presents a first approach to the metabolism of C. moewusii under conditions of H2 evolution. 'This work was supported by Landesamt fur Forschung NRW. MATERIALS AND METHODS C. moewusii, strain 11-5/10, from the Pflanzenphysiologisches Institut der Universitat Gottingen was grown and harvested as described elsewhere (14). Concentrated cell suspensions (6 x 107 cells/ml) were used throughout all experiments. Illumination was provided by two fluorescent lamps (Philips TL 40W-1/32) where necessary; the light intensity at the surface of t...

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confidence: 53%

Fermentative Metabolism of Hydrogen-evolving Chlamydomonas moewusii

Klein

Betz²

1978

Plant Physiol.

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“…Ferredoxin is as effective as methyl viologen in mediation of H2 evolution by dithionite oxidation with the same stabilized preparations of hydrogenase, a fact of significance for proposals to use the clostridial hydrogenase in solar energy bioconversion schemes (8,21,(26)(27)(28).…”

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confidence: 99%

A rationale for stabilization of oxygen-labile enzymes: application to a clostridial hydrogenase.

Klibanov¹,

Kaplan²,

Kamen³

1978

Proc. Natl. Acad. Sci. U.S.A.

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ABSTRACr A general procedure for stabilization of 02-labile enzymes exploiting "salting out" of oxygen from the microenvironment in the molecular layers immediately adjacent to charged surfaces of polyionic solid adsorbents has been develope. Empirical verification of this rationale is provided. The half-life of air inactivation of the Og-labile hydrogenase (EC 1.12.7.1) from Clostridium pasteurianum is increased 20-to 2-fold simply by adsorption (noncovalent binding) in dilute Tris-HCI buffer on common anion exchange supports such as DEAE-cellulose or Dowex 1-X2. Predicted increases in degree of stabilization by using more densely charged adsorbents (such as polyethyleneimine-cellulose), as well as bulkier solvent counter-anions, are found; half-lives for air inactivation for the bound hydrogenase can be increased to 3000-fold longer than that of the free enzyme. Most of the total catalytic activity, assayed as H2 evolution from dithionite mediated by methyl viologen or ferredoxin, is retained, whereas the expected suppression of H2 uptake in the reverse reaction is observed. Stabilization of the oxygen-labile hydrogenase (1) proposed for use in various schemes for bioconversion of solar energy (2) is critical for practical applications (3-5). Efforts to achieve stabilization to date (6-10) have been empirical, involving mainly immobilization of the enzyme (6, 9, 10), but success has been limited. It is known (1, 11) that the rate of 02 inactivation in solutions of the enzyme is directly proportional to 02 concentration. We have conceived a rationale based on exploitation of the well-known "salting out" phenomenon whereby the concentration of dissolved gases in aqueous solution is reduced as the salt concentration is increased (12). This effect is thought to be caused by competition between salt and gas for solvent, the salt component progressively removing water by hydration, thereby decreasing solvent volume available to the gas. Thus, a decrease of an order of magnitude in gas solubility occurs as solvent is saturated by salt (13,14). We are able to show that relatively simple procedures based on this fact can be developed to achieve increases in hydrogenase stability in air sufficient to meet the requirements for practical applications in solar energy bioconversion.Our rationale is that if hydrogenase, or any Orlabile enzyme, is attached to a polyionic surface (it must be polycationic for an acidic enzyme such as hydrogenase to be adsorbed), the enzyme molecules will be buried in a microenvironment equivalent to that provided by an extremely concentrated salt solution. There will be little solvent available for gas solution, so that access to the adsorbed enzyme will be minimal. In all probability, the salting out of gas may be much greater than is possible with saturated salt solutions because of solubility limitations. Hence the 02 concentration in such a microenvironment, extending several molecular layers from the charged adsorbent surface, will be very small so that a relatively large increase in 02 st...

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Hydrogen production by algae

Bothe

1982

New Trends in Research and Utilization of Solar Energy Through Biological Systems

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The Mechanism of Hydrogen Photoevolution in Photosynthetic Organisms

Cited by 8 publications

References 11 publications

Fermentative Metabolism of Hydrogen-evolving Chlamydomonas moewusii

Fermentative Metabolism of Hydrogen-evolving Chlamydomonas moewusii

A rationale for stabilization of oxygen-labile enzymes: application to a clostridial hydrogenase.

Hydrogen production by algae

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