Enhanced Incorporation of Tritium into Glycolate during Photosynthesis by Tobacco Leaf Tissue in the Presence of Tritiated Water

AUTOR(ES)

Peterson, Richard B.

RESUMO

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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