Aminoacyltransferase II from Rat Liver

Aminoacyltransferase II from rat liver has been purified to homogeneity by the criteria of disc gel electrophoresis and ultracentrifugation. The purified enzyme shows activity in the following assays: (a) incorporation of 14C-leucine into protein from 14C-leucyl-tRNA in the presence of aminoacyltransferase I, (b) ribosome-dependent hydrolysis of GTP-γ-33P, (c) stimulation of the reaction between polysomal nascent polypeptide chains and 3H-puromycin, and (d) 3H-adenosine diphosphoribose incorporation into the enzyme from 3H-NAD+ in the presence of diphtheria toxin. Unlike the other activities, the ribosome-dependent GTPase activity is separated, early in the purification, into two fractions. The minor fraction is that associated with aminoacyltransferase II, while the major one is distinct in many of its properties from the transfer factor. Approximately 1 mole of 3H-adenosine diphosphoribose can be covalently bound to 1 mole of the enzyme.