Aminoacyltransferase II from Rat Liver

Abstract

Abstract Purified aminoacyltransferase II was analyzed to determine molecular size and to investigate the possibility of subunits. The molecular weight was determined to be 87,500 by sedimentation-diffusion, 105,500 by high speed equilibrium ultracentrifugation, and 94,000 to 105,000 by gel filtration. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated one principal component of molecular weight 89,000. These results indicate that the enzyme consists of a single polypeptide chain of molecular weight 96,500 ± 9,000. The enzyme underwent a specific breakdown upon aging at 0–5deg; into components of approximately 64,000, 42,000, and 37,000. Various treatments were used in an attempt to speed the breakdown, but the resulting gel patterns were different from that produced by aging. Experiments with the 3H-adenosine diphosphoribose derivatives of the enzyme and of the breakdown products indicated that 3H-adenosine diphosphoribose was present in the undergraded enzyme and in one or both of the smaller breakdown components, but not in the 64,000 molecular weight component. Although both the undergraded enzyme and a fragment could accept 3H-adenosine diphosphoribose, no evidence for a fragment active in amino acid incorporation or in ribosome-dependent GTPase was obtained.