End product control of tryptophan biosynthesis in extracts and intact cells of the higher plant nicotina tabacum var. Wisconsin 38

Abstract

A study has been made of the control by end-product inhibition of the tryptophan biosynthetic pathway in cultured cells of the higher plant, Nicotiana tabacum, var. Wisconsin 38. Crude extracts of callus tissue obtained from N. tabacum catalyzed the conversion of chorismic acid to anthranilic acid, the first step unique to l-tryptophan version of chorismic acid to anthranilic acid, the first step unique to l-tryptophan biosynthesis. The catalytic activity was destroyed by heat and no reaction occured with the ommission of either glutamine of Mg 2+. In cell extracts this catalytic activity was inhibited by l-tryptophan. The inhibition was competitive with chorismate. In experiments with intact cells the presence of high l-tryptophan pools reduced the flow of radioactive carbon from the precursor, shikimic acid, into biosynthetic L-tryptophan. The data obtained were consistent with the operation of end-product inhibition in vivo