Isolation and Stoichiometry of Beef Pancreas Tryptophanyl‐tRNA Synthetase Complexes with Tryptophan and Tryptophanyladenylate

Abstract

Highly purified tryptophanyl‐tRNA synthetase from beef pancreas forms an enzymetryptophanyladenylate complex which has been isolated from reaction mixtures by gel filtration. The stoichiometry of the complex is 2 moles of tryptophanyladenylate per mole of native enzyme of 108000 molecular weight. The complex reacts with inorganic pyrophosphate to form 1 mole of ATP per mole of bound tryptophanyladenylate and with yeast‐tRNA to form tryptophanyl‐tRNA. An enzyme‐tryptophan complex can also be isolated by gel filtration. Its stability is lower than that of the enzyme‐tryptophanyladenylate complex. When the protein has been specially treated to remove bound tryptophan, no enzyme‐ATP complex can be isolated from a mixture of enzyme and ATP. The bound tryptophan can react stoichiometrically with ATP to give tryptophanyladenylate which remains bound to the enzyme.