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Title: Carbon Partitioning in Green Algae (Chlorophyta) and the Enolase Enzyme

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Journal Article: Published Article
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Journal Volume: 4; Journal Issue: 4; Related Information: CHORUS Timestamp: 2018-01-30 06:58:15; Journal ID: ISSN 2218-1989
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Polle, Jürgen, Neofotis, Peter, Huang, Andy, Chang, William, Sury, Kiran, and Wiech, Eliza. Carbon Partitioning in Green Algae (Chlorophyta) and the Enolase Enzyme. Switzerland: N. p., 2014. Web. doi:10.3390/metabo4030612.
Polle, Jürgen, Neofotis, Peter, Huang, Andy, Chang, William, Sury, Kiran, & Wiech, Eliza. Carbon Partitioning in Green Algae (Chlorophyta) and the Enolase Enzyme. Switzerland. doi:10.3390/metabo4030612.
Polle, Jürgen, Neofotis, Peter, Huang, Andy, Chang, William, Sury, Kiran, and Wiech, Eliza. Mon . "Carbon Partitioning in Green Algae (Chlorophyta) and the Enolase Enzyme". Switzerland. doi:10.3390/metabo4030612.
title = {Carbon Partitioning in Green Algae (Chlorophyta) and the Enolase Enzyme},
author = {Polle, Jürgen and Neofotis, Peter and Huang, Andy and Chang, William and Sury, Kiran and Wiech, Eliza},
abstractNote = {},
doi = {10.3390/metabo4030612},
journal = {Metabolites},
number = 4,
volume = 4,
place = {Switzerland},
year = {Mon Aug 04 00:00:00 EDT 2014},
month = {Mon Aug 04 00:00:00 EDT 2014}

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Publisher's Version of Record at 10.3390/metabo4030612

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  • The effects of ammonium assimilation on photosynthetic carbon fixation and O{sub 2} exchange were examined in two species of N-limited green algae, Chlorella pyrenoidosa and Selenastrum minutum. Under light-saturating conditions, ammonium assimilation resulted in a suppression of photosynthetic carbon fixation by S. minutum but not by C. pyrenoidosa. These different responses are due to different relationships between cellular ribulose bisphosphate (RuBP) concentration and the RuBP binding site density of ribulose bisphosphate carboxylase/oxygenase (Rubisco). In both species, ammonium assimilation resulted in a decrease in RuBP concentration. In S. minutum the concentration fell below the RuBP binding site density of Rubisco, indicatingmore » RuBP limitation of carboxylation. In contrast, RuBP concentration remained above the binding site density in C. pyrenoidosa. Compromising RuBP regeneration in C. pyrenoidosa with low light resulted in an ammonium-induced decrease in RuBP concentration below the RuBP binding site density of Rubisco. This resulted in a decrease in photosynthetic carbon fixation. In both species, ammonium assimilation resulted in a larger decrease in net O{sub 2} evolution than in carbon fixation. Mass spectrometric analysis shows this to be a result of an increase in the rate of mitochondrial respiration in the light.« less
  • Rates of photosynthetic O{sub 2} evolution, for measuring K{sub 0.5}(CO{sub 2} + HCO{sub 3}{sup {minus}}) at pH 7, upon addition of 50 micromolar HCO{sub 3}{sup {minus}} to air-adapted Chlamydomonas, Dunaliella, or Scenedesmus cells, were inhibited up to 90% by the addition of 1.5 to 4.0 millimolar salicylhydroxamic acid (SHAM) to the aqueous medium. The apparent K{sub i}(SHAM) for Chlamydomonas cells was about 2.5 millimolar, but due to low solubility in water effective concentrations would be lower. Salicylhydroxamic acid did not inhibit oxygen evolution or accumulation of bicarbonate by Scenedesmus cells between pH 8 to 11 or by isolated intact chloroplastsmore » from Dunaliella. Thus, salicylhydroxamic acid appears to inhibit CO{sub 2} uptake, whereas previous results indicate that vanadate inhibits bicarbonate uptake. These conclusions were confirmed by three test procedures with three air-adapted algae at pH 7. Salicylhydroxamic acid inhibited the cellular accumulation of dissolved inorganic carbon, the rate of photosynthetic O{sub 2} evolution dependent on low levels of dissolved inorganic carbon (50 micromolar NaHCO{sub 3}), and the rate of {sup 14}CO{sub 2} fixation with 100 micromolar ({sup 14}C)HCO{sub 3}{sup {minus}}. Salicylhydroxamic acid inhibition of O{sub 2} evolution and {sup 14}CO{sub 2}-fixation was reversed by higher levels of NaHCO{sub 3}. Thus, salicylhydroxamic acid inhibition was apparently not affecting steps of photosynthesis other than CO{sub 2} accumulation. Although salicylhydroxamic acid is an inhibitor of alternative respiration in algae, it is not known whether the two processes are related.« less
  • Several members of the green algae possess the ability to produce lipids and/or high value compounds in significant quantities. While for several of these green algal species induction of increased lipid production has been shown, and cultivation of species for high value molecules occurs at production scale, the molecular mechanisms governing over-accumulation of molecules synthesized from isoprenoid precursors, carotenoids, for example, have received far less attention. Here, we present a calculation of the required ATP equivalencies per carbon atom and reducing power equivalencies as NADH/NADPH (NAD(P)H) per carbon atom for the isoprenoid molecules ..beta..-carotene (C40), astaxanthin (C40), and squalene (C30).more » We compared energetic requirements of carbohydrates, triacylglycerol, and isoprenoid molecules under a gradient of conditions of cellular stress. Our calculations revealed slightly less ATP and NAD(P)H equivalency per carbon atom between triacylglycerol and the three isoprenoid molecules. Based on our results, we propose that the driving force for differences in accumulation patterns of carotenoids vs. triacylglycerols in algal cells under stress is largely dependent on the presence and regulation of bypass mechanisms at metabolic junction bottlenecks, like pyruvate dehydrogenase (PDH), within particular species. We provide a discussion of several molecular mechanisms that may influence carbon partitioning within different groups of green algae, including metabolic inhibition through accumulation of specific substrates related to ATP and reducing equivalent production (NAD(P)H) as well as cellular compartmentalization. This work contributes to the ongoing discussion of cellular homeostatic regulation during stress, as well as the potential mechanisms driving long-term carbon storage as it relates to energy and redox states within the algal cell.« less