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

The oxyhydrogen reaction in the presence and absence of CO(2) was studied in H(2)-adapted Scenedesmus obliquus by monitoring the initial rates of H(2), O(2), and (14)CO(2) uptake and the effect of inhibitors on these rates with gas-sensing electrodes and isotopic techniques. In the presence of 0.02 atmosphere O(2), the pH(2) was varied from 0 to 1 atmosphere. Whereas the rate of O(2) uptake increased by only 30%, the rate of H(2) uptake increased severalfold over the range of pH(2) values. At 0.1 atmosphere H(2) and 0.02 atmosphere O(2), rates for H(2) and O(2) uptake were between 15 and 25 micromoles per milligram chlorophyll per hour. As the pH(2) was changed from 0 to 1 atmosphere, the quotient H(2):O(2) changed from 0 to roughly 2. This change may reflect the competition between H(2) and the endogenous respiratory electron donors. Respiration in the presence of glucose and acetate was also competitive with H(2) uptake. KCN inhibited equally respiration (O(2) uptake in the absence of H(2)) and the oxyhydrogen reaction in the presence and absence of CO(2). 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 CO(2) 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.