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Amino Acid Transport into Cultured Tobacco Cells. I. Lysine Transport
H. Michael Harrington and Randolph R. Henke
Vol. 67, No. 2 (Feb., 1981), pp. 373-378
Published by: American Society of Plant Biologists (ASPB)
Stable URL: http://www.jstor.org/stable/4266650
Page Count: 6
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Lysine transport into suspension-cultured Wisconsin-38 tobacco cells was observed. Uptake was linear (up to 90 minutes) with respect to time and amount of tissue only after 4 to 6 hours preincubation in calcium-containing medium. The observed cellular accumulation of lysine was against a concentration gradient and not due to exchange diffusion. Transport was stimulated by low pH and characterized by a biphasic uptake isotherm with two Km values for lysine. System I (Km ≃ 5 × 10-6 molar; Vmax ≃ 180 nanomoles per gram fresh weight per hour) and system II (Km ≃ 10-4 molar; Vmax ≃ 1900 nanomoles per gram fresh weight per hour) were inhibited by N-ethylmaleimide and a variety of respiratory inhibitors. This inhibition was not due to increased efflux. In antagonism experiments, system I was inhibited most effectively by basic amino acids, followed by the sulfur amino acids. System I was only slightly inhibited by the neutral and aromatic amino acids and was not inhibited by the acidic amino acids aspartic and glutamic acids. Transport by system II was inhibited by all of the tested amino acids (including aspartic and glutamic acids) and analogs; however, this system was not inhibited by D-arginine. Neither system was strongly inhibited by D-lysine or the lysine analog S-2-aminoethyl-L-cysteine. Arginine was shown to be a competitive inhibitor of both systems with values for Ki similar to the respective Km values. These studies suggest the presence of at least two amino acid permeases in W-38 tobacco cells.
Plant Physiology © 1981 American Society of Plant Biologists (ASPB)