H2 Metabolism in Photosynthetic Organisms

Abstract

Dark H₂ metabolism was studied in marine and fresh water red algae, the green alga, Chlamydomonas, and mosses. A time variable and temperature-sensitive anaerobic incubation was required prior to H₂ evolution. H₂ evolution was sensitive to disalicylidenepropanediamine. An immediate H₂ uptake was observed in these algae. Immediate dark H₂ uptake but no evolution was observed in the mosses. A cell-free hydrogenase preparation was obtained from anaerobically adapted Chlamydomonas reinhardii by means of sonic oscillation. The hydrogenase was not sedimented at 100,000g. It catalyzed the reduction of methylene blue, p-benzoquinone, NAD, NADP, but not spinach ferredoxin. H₂ evolution was noted with dithionite and with reduced methyl viologen as donors but not with reduced spinach ferredoxin. Similarly, hydrogenase activities were not affected by disalicylidenepropanediamine. The pH optima for H₂ evolution and for H₂ uptake were 7.2 and 7.5 to 9.5, respectively. Extracts prepared from the anaerobically adapted red alga, Chondrus crispus, and the moss, Leptobryum pyriforme, consumed but did not evolve H₂. Uptake was slightly stimulated by methylene blue. It is proposed that red algae and mosses appear to metabolize H₂ by a different pathway than Chlamydomonas.