Tryptophan biosynthesis in Nicotiana tabacum and Daucus carota cell cultures: Site of action of inhibitory tryptophan analogs

Abstract

1. 1. Eight tryptophan analogs completely inhibit the growth of Nicotiana tabacum (tobacco) and Daucus carota (carrot) cells with 5-methyltryptophan, 4-methyltryptophan, 5-fluorotrytophan and 6-fluorotryptophan being the most effective with 5-hydroxytryptophan, 3β-indoleacrylic acid, 7-azatryptophan, and 3-methylanthranilic acid less effective. 2. 2. The growth inhibition caused by all the analogs, except 3β-indoleacrylic acid and 3-methylanthranilic acid, could be reversed by the addition to the medium of anthranilic acid, indole or l-tryptophan. 3. 3. Anthranilate synthetase, which is normally feedback inhibited by l-tryptophan, was much more sensitive to inhibition by all the analogs than was tryptophan synthetase. 4. 4. The evidence indicates that all of the analogs, except 3β-indoleacrylic acid and 3-methylanthranilic acid, act by inhibiting anthranilate synthetase which effectively stops the biosynthesis of tryptophan. The lack of tryptophan prevents cell growth.