^<14>CO_2 Labeling Studies of 2-Carboxyarabinitol 1-Phosphate Synthesis

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2-Carboxyarabinitol l-phosphate (CA1P) is involved in the regulation of ribulose 1,5-bis-phosphate carboxylase (rubisco) activity in many plants, but the biochemical pathway for its synthesis is unknown. In an attempt to induce synthesis of ^<14>C-CA1P in vivo, intact leaflets of Phaseolus vulgaris were pulse-labeled with ^<14>CO_2 and chased with ^<12>CO_2 under conditions which result in leaves accumulating unlabeled CA1P. Sugar-phosphates were isolated from leaf extracts by anion exchange chromatography and constituent metabolites were separated by 2D-thin-layer chromatography. No ^<14>C-labeled CA1P was recovered from extracts prepared from leaves experiencing a range of exposure/chase conditions, a range of leaf/plant ages, or from other species differing in their ability to accumulate unlabeled CA1P. Appropriate control experiments indicated no loss of ^<14>C-standard which had been added at the time of killing the leaf. The data suggest that carboxyarabinitol 1-phosphate is not synthesized in vivo as some "misfire" catalysis by rubisco and that the precursor to its synthesis is far "downstream" of CO_2 fixation.
日本植物生理学会の論文