Molecular Enzymology of Beef Pancreas Tryptophanyl-tRNA Synthetase

Abstract

Tryptophanyl-tRNA synthetase was the first aminoacyl-tRNA synthetase to be partially purified, the result of pioneering work done in Lipmann’s laboratory (Davie et al. 1956). Later this enzyme became the subject of intensive study in the laboratory of Bernard and Julie Labouesse (Université de Bordeaux II) and in our laboratory. The parallel investigations of these two groups complement and enrich each other. Part of their work was summarized by Kisselev et al. (1978a).

The aim of this paper is to review briefly current results, including those of our colleagues (see Acknowledgments), obtained with tryptophanyl-tRNA synthetase.

ISOLATION AND CHARACTERIZATION OF THE TRYPTOPHANYL ENZYME
We have identified, isolated, and characterized a covalent derivative formed between the tryptophan residue and beef pancreas tryptophanyl-tRNA synthetase (Kovaleva et al. 1976Kovaleva et al. 1978a; Favorova et al. 1978). One mole or less of the tryptophan residues is covalently bound per mole of the dimeric enzyme. The tryptophan residue in this derivative is believed to be in the activated state because it (1) exchanges with exogenous tryptophan rather than with other amino acids, (2) reacts with NH₂OH yielding a tryptophanyl hydroxylamine, and (3) aminoacylates tRNA^Trp in the absence of ATP (other tRNAs are not aminoacylated). The tryptophanyl enzyme is decomposed during incubation with AMP or pyrophosphate.

The energy-rich bond that makes it possible for the tryptophan in the tryptophanyl enzyme to be substituted by free tryptophan with a protonated amino group may be an anhydrous one (Bender 1960).

It is known that NH₂OH reacts with mixed anhydrides of carboxylic acids...