Non-cyclic photoreductive carbon fixation in photosynthesis. Light and dark transients of the glycerate-3-P special pair.
It is demonstrated that carbon fixation in photosynthesis is regulated in two kinetically coupled pathways involving the specialized pair of non-equivalent, enzyme-bound glycerate-3-P (3-PGA) molecules obtained from ribulose 1,5-bisphosphate (RuBP) carboxylation in the light. A non-cyclic pathway is suggested (reaction 2) for the direct biosynthesis of sucrose from the 3-PGA obtained from C-3, C-4 and C-5 of the six-carbon carboxylation adduct. Concomitant to the appearance of sucrose as the principal product, the Mg2+-bound 3-PGA molecule formed from C-1, C-2 and C-2' of the C6 intermediate is released and subsequently reduced in regenerating the RuBP. It is proposed that the nocturnal inhibitor, 2-carboxyarabinitol-1-phosphate (1-PCA) is obtained from a condensation of 3-PGA and glyceraldehyde.
Fong
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FK
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907.
Butcher
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KA
D002244:Carbon / Q000378:metabolism*; D003624:Darkness; D005988:Glyceric Acids / Q000378:metabolism*; D008027:Light; D008274:Magnesium / Q000378:metabolism; D008968:Molecular Conformation; D010428:Pentosephosphates / Q000378:metabolism; D010788:Photosynthesis; D010944:Plants / Q000378:metabolism*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D012274:Ribulosephosphates / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism
D005988:Glyceric Acids; D010428:Pentosephosphates; D012274:Ribulosephosphates; C054549:2-carboxyarabinitol 1-phosphate; C001933:ribulose-1,5 diphosphate; D013395:Sucrose; D002244:Carbon; C005156:3-phosphoglycerate; D012273:Ribulose-Bisphosphate Carboxylase; D008274:Magnesium