期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：47
页码：29629-29636
DOI：10.1073/pnas.2009210117
出版社：The National Academy of Sciences of the United States of America
摘要：The unicellular green alga Chlamydomonas reinhardtii is capable of photosynthetic H 2 production. H 2 evolution occurs under anaerobic conditions and is difficult to sustain due to 1) competition between [FeFe]-hydrogenase (H 2 ase), the key enzyme responsible for H 2 metabolism in algae, and the Calvin–Benson–Bassham (CBB) cycle for photosynthetic reductants and 2) inactivation of H 2 ase by O 2 coevolved in photosynthesis. Recently, we achieved sustainable H 2 photoproduction by shifting algae from continuous illumination to a train of short (1 s) light pulses, interrupted by longer (9 s) dark periods. This illumination regime prevents activation of the CBB cycle and redirects photosynthetic electrons to H 2 ase. Employing membrane-inlet mass spectrometry and H 2 18 O , we now present clear evidence that efficient H 2 photoproduction in pulse-illuminated algae depends primarily on direct water biophotolysis, where water oxidation at the donor side of photosystem II (PSII) provides electrons for the reduction of protons by H 2 ase downstream of photosystem I. This occurs exclusively in the absence of CO 2 fixation, while with the activation of the CBB cycle by longer (8 s) light pulses the H 2 photoproduction ceases and instead a slow overall H 2 uptake is observed. We also demonstrate that the loss of PSII activity in DCMU-treated algae or in PSII-deficient mutant cells can be partly compensated for by the indirect (PSII-independent) H 2 photoproduction pathway, but only for a short (<1 h) period. Thus, PSII activity is indispensable for a sustained process, where it is responsible for more than 92% of the final H 2 yield.
关键词：green algae ; hydrogen production ; water splitting ; carbon dioxide ; hydrogenase
