BEEF PANCREAS TRYPTOPHANYL-TRNA SYNTHETASE - MOLECULAR WEIGHT, COMPOSITION AND SPECTRAL PROPERTIES

The molecular weight of beef pancreatic tryptophanyl‐tRNA synthetase has been determined by Sephadex filtration, by equilibrium sedimentation according to Yphantis and to Van Holde and Baldwin, and by light scattering. These different techniques indicate an average molecular weight of 108000. The amino acid composition has been determined after total acid hydrolysis of the performic acid oxidized and of the carboxymethylated reduced protein. Spectrophotometric measurements, according to Edelhoch, have been used for tryptophan determination. The cysteine and cystine content have been measured before and after reduction by sodium borohydride in urea. From this study it is concluded that tryptophanyl‐tRNA synthetase contains no disulfide bridge. Its molecular extinction coefficient at 280 nm is 9 × 104. The optical rotatory dispersion of the enzyme indicates that it contains about a third of its polypeptide chain in helical conformation. Copyright © 1969, Wiley Blackwell. All rights reserved