title: The glucose 6-phosphate shunt around the Calvin-Benson cycle.
abstract: It is just over 60 years since a cycle for the regeneration of the CO2-acceptor used in photosynthesis was proposed. In this opinion paper, we revisit the origins of the Calvin-Benson cycle that occurred at the time that the hexose monophosphate shunt, now called the pentose phosphate pathway, was being worked out. Eventually the pentose phosphate pathway was separated into two branches, an oxidative branch and a non-oxidative branch. It is generally thought that the Calvin-Benson cycle is the reverse of the non-oxidative branch of the pentose phosphate pathway but we describe crucial differences and also propose that some carbon routinely passes through the oxidative branch of the pentose phosphate pathway. This creates a futile cycle but may help to stabilize photosynthesis. If it occurs it could explain a number of enigmas including the lack of complete labelling of the Calvin-Benson cycle intermediates when carbon isotopes are fed to photosynthesizing leaves.
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA tsharkey@msu.edu.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Sharkey
authors.affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Sean E
authors.initials: SE
authors.lastname: Weise
mesh_terms: D019298:Glucose-6-Phosphate / Q000378:metabolism*; D053858:Metabolic Networks and Pathways / Q000502:physiology; D008954:Models, Biological; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology
chemical_list: D019298:Glucose-6-Phosphate
keywords: Calvin–Benson cycle; cyclic electron flow; energetics; oxidative pentose phosphate pathway; reductive pentose phosphate pathway; starch synthesis.