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The Gas Exchange of Hydrogen-adapted Algae as Followed by Mass Spectrometry ¹

^a Institute of Molecular Biophysics, Department of Biological Science, Florida State University, Tallahassee, Florida 32306

A mass spectrometer inlet and an oxygen electrode in the same vessel allowed the continuous recording of the gases exchanged (H₂, CO₂, O₂) by hydrogenase-containing anaerobically adapted Scenedesmus obliquus strain D₃ (Gaffron) and Chlorella fusca Shihira et Krauss (= pyrenoidosa) 211-15. A light intensity which produces more photosynthetic oxygen than the cells can re-reduce to water leads to de-adaptation and the substitution of normal photosynthesis for photoreduction. The sequence of these metabolic events was recorded in a matter of a few minutes. Upon exposure of these adapted algae to light, an evolution of hydrogen lasting up to 60 seconds preceded any other light-dependent gas exchange. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, this initial hydrogen production was inhibited approximately 50%, pointing to a contribution of electrons by photosystem II. At very low hydrogen tensions (0.1 microliter per milliliter), a balance between light-induced production and absorption of hydrogen was observed in normal, unpoisoned algae. Addition of either glucose or inhibitors of phosphorylation increased the release of hydrogen in the light very considerably. When the light was turned off the algae consumed the remaining amount of hydrogen, only to release it again upon illumination. This reversible hydrogen exchange persisted even when any concomitant carbon dioxide exchange had been abolished.