STUDIES ON VALYL-TRNA SYNTHETASE AND TRNAVAL FROM ESCHERICHIA COLI .I. PURIFICATION AND PROPERTIES OF ENZYME FROM NORMAL ESCHERICHIA COLI STRAINS

A highly purified valyl-tRNA synthetase was prepared from Escherichia coli K12 strain. A sedimentation coefficient (Sw20) of 5.6 s and a molecular weight of 110,000 were determined. One active site for valine and ATP was detected. Binding of these substrates to the active site changed the number of SH groups titrated. Some indications were found for a conformational change induced by an aminoacyl-AMP analog. Antiserum prepared against the pure enzyme inhibited all the activity in extracts, indicating the existence of one activating enzyme for valine in E. coli. No immunological cross-reaction was detected between valyl and isoleucyl activating enzymes in spite of similarities in structure and substrate recognition. © 1969.