A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
Effects of extracellular pH on the metabolic pathways in sulfur-deprived, H-2-producing Chlamydomonas reinhardtii cultures
Tekijät: Kosourov S, Seibert M, Ghirardi ML
Kustantaja: OXFORD UNIV PRESS
Julkaisuvuosi: 2003
Journal: Plant and Cell Physiology
Tietokannassa oleva lehden nimi: PLANT AND CELL PHYSIOLOGY
Lehden akronyymi: PLANT CELL PHYSIOL
Vuosikerta: 44
Numero: 2
Aloitussivu: 146
Lopetussivu: 155
Sivujen määrä: 10
ISSN: 0032-0781
DOI: https://doi.org/10.1093/pcp/pcg020
Tiivistelmä
Sustained photoproduction of H, by the green alga, Chlamydomonas reinhardtii, can be obtained by incubating cells in sulfur-deprived medium [Ghirardi et al. (2000b) Trends BiotechnoL 18: 506; Melis et al. (2000) Plant Physiol. 122: 127]. The current work focuses on (a) the effects of different initial extracellular pHs on the inactivation of photosystem II (PSII) and O-2-sensitive H-2-production activity in sulfur-deprived algal cells and (b) the relationships among H-2-production, photosynthetic, aerobic and anaerobic metabolisms under different pH regimens. The maximum rate and yield of H-2 production occur when the pH at the start of the sulfur deprivation period is 7.7 and decrease when the initial pH is lowered to 6.5 or increased to 8.2. The pH profile of hydrogen photoproduction correlates with that of the residual PSII activity (optimum pH 7.3-7.9), but not with the pH profiles of photosynthetic electron transport through photosystem I or of starch and protein degradation. In vitro hydrogenase activity over this pH range is much higher than the actual in situ rates of H-2 production, indicating that hydrogenase activity per se is not limiting. Starch and protein catabolisms generate formate, acetate and ethanol; contribute some reductant for H-2 photoproduction, as indicated by 3-(3,4-dichlorophenyl)1,1-dimethylurea and 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone inhibition results; and are the primary sources of reductant for respiratory processes that remove photo-synthetically generated O-2. Carbon balances demonstrate that alternative metabolic pathways predominate at different pHs, and these depend on whether residual photosynthetic activity is present or not.
Sustained photoproduction of H, by the green alga, Chlamydomonas reinhardtii, can be obtained by incubating cells in sulfur-deprived medium [Ghirardi et al. (2000b) Trends BiotechnoL 18: 506; Melis et al. (2000) Plant Physiol. 122: 127]. The current work focuses on (a) the effects of different initial extracellular pHs on the inactivation of photosystem II (PSII) and O-2-sensitive H-2-production activity in sulfur-deprived algal cells and (b) the relationships among H-2-production, photosynthetic, aerobic and anaerobic metabolisms under different pH regimens. The maximum rate and yield of H-2 production occur when the pH at the start of the sulfur deprivation period is 7.7 and decrease when the initial pH is lowered to 6.5 or increased to 8.2. The pH profile of hydrogen photoproduction correlates with that of the residual PSII activity (optimum pH 7.3-7.9), but not with the pH profiles of photosynthetic electron transport through photosystem I or of starch and protein degradation. In vitro hydrogenase activity over this pH range is much higher than the actual in situ rates of H-2 production, indicating that hydrogenase activity per se is not limiting. Starch and protein catabolisms generate formate, acetate and ethanol; contribute some reductant for H-2 photoproduction, as indicated by 3-(3,4-dichlorophenyl)1,1-dimethylurea and 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone inhibition results; and are the primary sources of reductant for respiratory processes that remove photo-synthetically generated O-2. Carbon balances demonstrate that alternative metabolic pathways predominate at different pHs, and these depend on whether residual photosynthetic activity is present or not.
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