The activity and sedimentation properties of the aminoacyl-tRNA synthet ases of rat skeletal muscle

The aminoacyl-tRNA synthetases of the postribosomal supernatant fraction of rat skeletal muscle were characterized by their activity and sedimentation properties. The synthetases of muscle were compared with those of liver in terms of these parameters. Extraction of the synthetases of muscle with a buffer containing 4 mM adenosine triphosphate (ATP) resulted in a 50–100% increase in the activities of glutaminyl-, glutamyl-, isoleucyl-, leucyl-, lysyl-, methionyl- and prolyl-tRNA synthetases in the posrtibosomal fraction, over those activities extracted in the absence of ATP. This effect of ATP was specific for those synthetases which sedimented as particulate elements in sucrose gradients, and appeared to be unique to muscle. The individual synthetase activities of muscle, except alanyl-, leucyl- and valyl-tRNA synthetases, were approx. 25% of the corresponding synthetase activities of liver. Sucrose density gradient analysis of the postribosomal fraction of muscle and liver revealed that the sedimentation profiles of the synthetases of the two tissues were similar, with nine synthetase activities sedimenting as large particulate entities at 18 S. The findings suggest that the particulate forms of the synthetases reflect true association of the enzymes with a high molecular weight cellular component common to both tissues.