In Vivo Conversion of 5-Oxoproline to Glutamate by Higher Plants

Abstract

l-(U-(14)C)-5-oxoproline (pyrollidone carboxylic acid or pyroglutamic acid) was infiltrated into detached leaves of a number of species and incubated for 1 to 6 hours. In every case, conversion to labeled glutamate and glutamine was observed. The amount converted varied from 1 to 64% of the total label fed depending on the species. The ratio of glutamate-(14)C to glutamine-(14)C ranged from 5 in Vicia faba to 1 in sugar beet. This ratio could be affected by preinfiltrating various compounds before allowing the uptake of the 5-oxoproline. When l-methionine-dl-sulfoximine was prefed to sugar beet leaves, the glutamate-glutamine ratio increased from 1 to 10. Prior treatment of V. faba leaves with azaserine resulted in essentially only labeled glutamine being recovered. Preinfiltration with NaF or ATP gave similar results in that the glutamate-glutamine ratio was greatly decreased. The results are consistent with glutamate being produced from the 5-oxoproline and then being converted to glutamine.