Pentose Phosphate Pathway Reactions in Photosynthesizing Cells

Sharkey, Thomas D.

doi:10.3390/cells10061547

Title: Pentose Phosphate Pathway Reactions in Photosynthesizing Cells

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Abstract

The pentose phosphate pathway (PPP) is divided into an oxidative branch that makes pentose phosphates and a non-oxidative branch that consumes pentose phosphates, though the non-oxidative branch is considered reversible. A modified version of the non-oxidative branch is a critical component of the Calvin–Benson cycle that converts CO₂ into sugar. The reaction sequence in the Calvin–Benson cycle is from triose phosphates to pentose phosphates, the opposite of the typical direction of the non-oxidative PPP. The photosynthetic direction is favored by replacing the transaldolase step of the normal non-oxidative PPP with a second aldolase reaction plus sedoheptulose-1,7-bisphosphatase. This can be considered an anabolic version of the non-oxidative PPP and is found in a few situations other than photosynthesis. In addition to the strong association of the non-oxidative PPP with photosynthesis metabolism, there is recent evidence that the oxidative PPP reactions are also important in photosynthesizing cells. These reactions can form a shunt around the non-oxidative PPP section of the Calvin–Benson cycle, consuming three ATP per glucose 6-phosphate consumed. A constitutive operation of this shunt occurs in the cytosol and gives rise to an unusual labeling pattern of photosynthetic metabolites while an inducible shunt in the stroma may occur in response tomore » stress.« less

Authors:: Sharkey, Thomas D.

Publication Date:: Fri Jun 18 00:00:00 EDT 2021

Research Org.:: Michigan State Univ., East Lansing, MI (United States)

Sponsoring Org.:: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF)

OSTI Identifier:: 1797840

Alternate Identifier(s):: OSTI ID: 1850001

Grant/Contract Number:: FG02-91ER20021; 2022495

Resource Type:: Published Article

Journal Name:: Cells

Additional Journal Information:: Journal Name: Cells Journal Volume: 10 Journal Issue: 6; Journal ID: ISSN 2073-4409

Publisher:: MDPI AG

Country of Publication:: Switzerland

Language:: English

Subject:: 59 BASIC BIOLOGICAL SCIENCES; Cell Biology; 13C; 14C; aldol; Calvin-Benson cycle; light respiration; photosynthesis; isotope labeling

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                    Sharkey, Thomas D. Pentose Phosphate Pathway Reactions in Photosynthesizing Cells.  Switzerland: N. p., 2021. 
Web.  doi:10.3390/cells10061547.

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                    Sharkey, Thomas D. Pentose Phosphate Pathway Reactions in Photosynthesizing Cells.  Switzerland.  https://doi.org/10.3390/cells10061547

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                    Sharkey, Thomas D. Fri .  
"Pentose Phosphate Pathway Reactions in Photosynthesizing Cells".  Switzerland.  https://doi.org/10.3390/cells10061547.

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@article{osti_1797840,

  title        = {Pentose Phosphate Pathway Reactions in Photosynthesizing Cells},

  author       = {Sharkey, Thomas D.},

  abstractNote = {The pentose phosphate pathway (PPP) is divided into an oxidative branch that makes pentose phosphates and a non-oxidative branch that consumes pentose phosphates, though the non-oxidative branch is considered reversible. A modified version of the non-oxidative branch is a critical component of the Calvin–Benson cycle that converts CO2 into sugar. The reaction sequence in the Calvin–Benson cycle is from triose phosphates to pentose phosphates, the opposite of the typical direction of the non-oxidative PPP. The photosynthetic direction is favored by replacing the transaldolase step of the normal non-oxidative PPP with a second aldolase reaction plus sedoheptulose-1,7-bisphosphatase. This can be considered an anabolic version of the non-oxidative PPP and is found in a few situations other than photosynthesis. In addition to the strong association of the non-oxidative PPP with photosynthesis metabolism, there is recent evidence that the oxidative PPP reactions are also important in photosynthesizing cells. These reactions can form a shunt around the non-oxidative PPP section of the Calvin–Benson cycle, consuming three ATP per glucose 6-phosphate consumed. A constitutive operation of this shunt occurs in the cytosol and gives rise to an unusual labeling pattern of photosynthetic metabolites while an inducible shunt in the stroma may occur in response to stress.},

  doi          = {10.3390/cells10061547},

  journal      = {Cells},

  number       = 6,

  volume       = 10,

  place        = {Switzerland},

  year         = {Fri Jun 18 00:00:00 EDT 2021},

  month        = {Fri Jun 18 00:00:00 EDT 2021}

}

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