Enhanced Incorporation of Tritium into Glycolate during Photosynthesis by Tobacco Leaf Tissue in the Presence of Tritiated Water |
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Authors: | Peterson R B |
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Institution: | Department of Biochemistry and Genetics, The Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504. |
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Abstract: | Tobacco (Nicotiana tabacum var. Havana Seed) leaf discs were allowed to photosynthesize for 3 to 20 minutes in the presence of 14CO2 and 3H2O. Several metabolites of the Calvin cycle and photorespiratory pathway were isolated and purified and the 3H:14C values measured. Glycolate had a 5- to 10-fold higher 3H:14C than the Calvin cycle intermediate 3-phosphoglyceric acid, or its end product sucrose. The glycolate oxidase inhibitor α-hydroxy-2-pyridinemethanesulfonic acid caused glycolate to accumulate in the tissue and lowered the 3H:14C in glycolate to a value similar to that in 3-phosphoglyceric acid. Phosphoglycolate, a possible precursor of glycolate arising from the Calvin cycle, exhibited a 3H:14C value similar to 3-phosphoglyceric acid under all conditions. The finding of a 3H enrichment in glycolate suggests that another source of glycolate, possibly the reduction of glyoxylate, exists in leaf tissue. Analyses of incorporation of 3H into the pro-2R and pro-2S hydrogens of glycolate, in the presence and absence of α-hydroxy-2-pyridinemethanesulfonic acid, suggest an alternative source of glycolate. Biochemical mechanisms to account for 3H enrichment into glycolate are evaluated. |
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