Tryptophanyl Transfer Ribonucleic Acid Synthetase of Escherichia coli

Abstract Tryptophanyl-tRNA synthetase of Escherichia coli B was purified 1000-fold by MnCl2 precipitation and column chromatography on DEAE-cellulose, hydroxylapatite, and Amberlite CG-50. The purified enzyme gave one peak of constant specific activity on Sephadex G-200, one protein band on disc gel electrophoresis, and contained no other aminoacyl-tRNA synthetases. The rate of tryptophanyl-tRNA formation was optimal at pH 8.8. The kinetic constants for tryptophan, ATP, and tRNAtrp were determined at pH 7.0 and 8.8, and the turnover number was 1200 at pH 8.8. The amino acid composition is similar to the composition of other aminoacyl-tRNA synthetases, except for a low tryptophan and half-cystine content. tRNAtrp was purified on benzoylated DEAE-cellulose and hydroxylapatite columns. The final product had a specific activity of 1.8 nmoles per A260 unit and an estimated purity of 100%. The calculated ratio of tRNAtrp to tryptophanyl-tRNA synthetase in vivo is 1:1.