Abstract
Highly purified isoleucyl-RNA synthetase from Escherichia coli forms both enzyme-isoleucyl adenylate and enzyme-valyl adenylate complexes. Both isolated complexes react with inorganic pyrophosphate to form adenosine-triphosphate (ATP). Only the isoleucyl adenylate complex transfers its aminoacyl moiety to t-RNA. Transfer RNA containing active isoleucine-specific chains induces breakdown of the enzyme-valyl adenylate complex.