Reduction of Carbon Dioxide Coupled With the Oxyhydrogen Reaction in Algae

Abstract

1. Unicellular algae possessing a hydrogenase system (Scenedesmus and other species), and having been adapted by anaerobic incubation to the hydrogen metabolism, reduce oxygen to water according to the equation O2 + 2H2 → 2H2O. 2. The oxyhydrogen reaction proceeds undisturbed only in the presence of carbon dioxide, which simultaneously is reduced according to the equation CO2 + 2H2 → H2O + (CH2O) = (carbohydrate). 3. The maximum yield of the induced reduction is one-half molecule of carbon dioxide reduced for each molecule of oxygen absorbed. 4. Partial reactions are recognizable in the course of the formation of water and it is with the absorption of the second equivalent of hydrogen that the carbon dioxide reduction appears to be coupled. 5. The velocity of the reaction increases in proportion to the partial pressure of oxygen, but only up to a certain point where any excess of oxygen causes the inactivation of the hydrogenase system. The reaction then ends prematurely. 6. During the oxyhydrogen reaction little or no oxygen is consumed for normal respiratory processes. 7. Small concentrations of cyanide, affecting neither photosynthesis nor photoreduction in the same cells, first inhibit the induced reduction of carbon dioxide and then lead to a complete inactivation of the hydrogenase system. 8. Hydroxylamine, added after adaptation, has either no inhibitory effect at all, or prevents solely the induced reduction of carbon dioxide without inactivating the hydrogenase system. 9. Dinitrophenol prevents the dark reduction of carbon dioxide while the reduction of oxygen continues to the formation of water. 10. Glucose diminishes the absorption of hydrogen, probably in its capacity as a competing hydrogen donor. 11. The induced reduction of carbon dioxide can be described as an oxido-reduction similar to that produced photochemically in the same cells.

Uptake of Carbon Dioxide, Hydrogen and Oxygen by Hydrogenomonas facilis

“…Since the solubilities of 0, and H, are small and numerically close: agpo = 0.02 and agso = 0.03 the oxygen constant KO, was employed for both gases (as was done by Gaffron, 1942) as well as in the computations for the volume of alkali added through the vent.…”

Some Effects of 2537 Å on Green Algae and Chloroplast Preparations

“…Scenedesmus and certain other green algae possess a latent hydrogenase system which can be activated by anaerobic incubation in darkness; this was discovered and studied in detail by Gaffron (8,9,18,23,24). Such adapted algae can reduce CO2 by two processes which can be measured manometrically.…”

Kinetics of the Oxyhydrogen Reaction in the Presence and Absence of Carbon Dioxide in Scenedesmus obliquus

“…The oxyhydrogen reaction in green algae, a process first noted and studied in depth by Gaffron (5), involves a simultaneous uptake of H2 and 02 under darkness. Using Warburg manometric techniques, he usually observed a quotient of H2:02 equal to 1.…”

“…In the presence of CO2, uptake of CO2 was observed and the quotient H2:02 changed to 2. To account for these stoichiometries, perturbation of the quotient with inhibitors and the release of only traces of CO2 during the oxyhydrogen reaction, Gaffron (5) concluded that little of the 02 absorbed by the algal cell in the presence of H2 was used for normal respiratory processes. Horwitz (11) used a mass spectrometer to monitor 02 and CO2 levels continuously and observed that both cellular respiration and the oxyhydrogen reaction coupled to CO2 reduction had the same dependence on 02 tension and that rates of 02 uptake for the two reactions fell within the same range.…”

“…Gaffron (5) observed that the addition of CO2 did influence the quantities of H2 and 02 consumed. Combining our observations with those of Gaffron indicates that H2-related metabolism in Scenedesmus may change with time and with the growth conditions used for the algae.…”