N5-Formyltetrahydrofolate counteracts methotrexate toxicity in tobacco cell culture |
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Authors: | Gary L. Creason Robert A. Gonzales |
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Affiliation: | (1) The Samuel Roberts Noble Foundation, 73402 Armore, OK, USA;(2) Present address: EniChem Americas, 2000 Princeton Park, Corporate Center, 08852 Monmouth Junction, NJ, USA |
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Abstract: | N5-Formyltetrahydrofolate (leucovorin) counteracted methotrexate toxicity in suspension cultures of Nicotiana tabacum var. Xanthi. Methotrexate at 50 nM inhibited growth of the tobacco cell cultures by 87%. Leucovorin at 200 uM reduced growth inhibition in methotrexate-treated cultures to 37%, but only if exogenous adenine and thymidine were simultaneously provided. In the absence of leucovorin, neither adenine plus thymidine, nor adenine plus thymidine plus methionine gave appreciable relief from methotrexate toxicity. Uptake of radioactive methotrexate at 50 nM was linear for at least 7 h. Uptake of methotrexate appeared to be saturable, with a Km of 50 uM and a Vmax of 1 nmol h–1 g–1 fresh weight. Leucovorin showed competitive inhibition of methotrexate uptake, having a Ki of 400 uM.Abbreviations ade adenine - MS Murashige and Skoog - MTX methotrexate - thd thymidine |
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