Threonyl-tRNA synthetase was purified ∼500-fold from a high-speed supernatant fraction of rat liver. The purified enzyme was estimated to be >95% pure from acrylamide gel electrophoresis under denaturing and nondenaturing conditions. Based on a native molecular weight from sedimentation equilibrium of 154 000 and a subunit molecular weight of 85 000 obtained by sodium dodecyl sulfate gel electrophoresis, the protein appears to be an α2 dimer. The α2 structure was also supported by cross-linking studies of the native enzyme. The purified protein has an s20,w of 7.2 and an isoelectric point of 6.4. Amino acid analyses revealed no unusual features, but attempts at automated sequence analyses suggested that both amino termini are blocked. Preliminary carbohydrate analyses suggested that the enzyme is a glycoprotein. Antibodies were raised against the purified protein which could inactivate and precipitate threonyl-tRNA synthetase.
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