Kinetics of the Oxyhydrogen Reaction in the Presence and Absence of Carbon Dioxide in Scenedesmus obliquus1

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The oxyhydrogen reaction in the presence and absence of CO2 was studied in H2-adapted Scenedesmus obliquus by monitoring the initial rates of H2, O2, and 14CO2 uptake and the effect of inhibitors on these rates with gas-sensing electrodes and isotopic techniques. In the presence of 0.02 atmosphere O2, the pH2 was varied from 0 to 1 atmosphere. Whereas the rate of O2 uptake increased by only 30%, the rate of H2 uptake increased severalfold over the range of pH2 values. At 0.1 atmosphere H2 and 0.02 atmosphere O2, rates for H2 and O2 uptake were between 15 and 25 micromoles per milligram chlorophyll per hour. As the pH2 was changed from 0 to 1 atmosphere, the quotient H2:O2 changed from 0 to roughly 2. This change may reflect the competition between H2 and the endogenous respiratory electron donors. Respiration in the presence of glucose and acetate was also competitive with H2 uptake. KCN inhibited equally respiration (O2 uptake in the absence of H2) and the oxyhydrogen reaction in the presence and absence of CO2. The uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone accelerated the rate of respiration and the oxyhydrogen reaction to a similar extent. It was concluded that the oxyhydrogen reaction both in the presence and absence of CO2 has properties in common with components of respiration and photosynthesis. Participation of these two processes in the oxyhydrogen reaction would require a closely linked shuttle between mitochondrion and chloroplast.

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