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Change in the Proportion of Two Aspartokinases in Carrot Root Tissue in Response to in Vitro Culture ¹

Department of Botany, Faculty of Science, University of Tokyo, Hongo, Tokyo, Japan

Two isofunctional aspartokinases (EC 2.7.2.4) exist in fresh root tissue of carrot (Daucus carota, cv. Oogata sanzun). The threoninesensitive portion constitutes about 70% of the activity; the lysinesensitive, less than 20%. Culture of slices of carrot tissue for 3 days reversed the ratio as the lysine-sensitive activity preferentially increased. Inhibition by threonine and lysine was additive in both enzyme preparations from fresh and cultured tissues. The activities were resolved into two distinct fractions of different sensitivity to threonine and lysine by DEAE-Sephadex A-50 column chromatography.