Thymidylate Synthase in Plant Cells : Kinetic and Molecular Properties of the Enzyme from Daucus carota L. Cell Cultures

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Thymidylate synthase activity was assayed in cell homogenates from wild or domestic carrot (Daucus carota L.) suspension cultures using the tritium-release method. The specific activity measured was lower than that previously reported for bacterial extracts, and its level did not change a great deal during a 14day growth cycle. The enzyme was partially purified (about 9 fold) by ammonium sulfate fractionation and ion-exchange chromatography. Kinetic parameters such as pH optimum, K_m values for substrate and cofactor, and degree of inhibition by 5-fluoro-2'-deoxyuridine monophosphate were characterized. The apparent mol wt, evaluated by gel-filtration chromatography, was 185 kDa, which was much higher than that reported for enzymes of bacterial and vertebrate origins and somewhat higher than that reported for the thymidylate synthase-dihydrofolate reductase bifunctional poly-peptide of some protozoa.
日本植物生理学会の論文