Altered lysine uptake by a variant carrot cell strain resistant to the lysine analog S-2-aminoethyl-L-cysteine

Summary C81 is a variant carrot ( Daucus carota L. cv. Danvers) cell strain selected for resistance to the lysine analog S-2-aminoethyl-L-cysteine (AEC). The resistance is due to decreased uptake of the analog (Matthews et al., 1980). AEC inhibition reversal experiments and lysine uptake inhibition experiments demonstrated that the basic amino acids arginine and lysine in addition to AEC are taken into carrot cells via the same carrier system. Nonpolar (leucine, proline and tryptophan), uncharged (asparagine), and acidic (aspartic acid and glutamic acid) amino acids are not taken up by this carrier system. Arginine inhibited lysine uptake in wild-type cells twice as much as did AEC, but no difference in lysine uptake inhibition by arginine and AEC was detected in the C81 cell variant. These data suggest that the lysine/arginine carrier system is altered in the C81 cell line. Lysine and AEC uptake studies suggest that the altered uptake capacity of C81 results from a decrease in affinity for both AEC and lysine, while the V max also appears to increase only when AEC is a substrate.