Rat liver polysome N alpha-acetyltransferase: isolation and characterization

Rat liver polysome N alpha-acetyltransferase has been purified to homogeneity by a four-step procedure that utilizes ammonium sulfate precipitation, gel filtration, hydroxylapatite chromatography, and Mono Q ion exchange chromatography. The enzyme is greatly stabilized by the inclusion of EDTA and 0.01% deoxycholate in the isolation buffers. The purified enzyme has a native molecular weight of 190,000 and a subunit molecular weight of 95,000, suggesting that it is a homodimer. The enzyme shows a pH optimum of 8.0 and is strongly inhibited by Cl-, I-, SCN-, and ClO4- and to a lesser degree by sulfate and acetate. It is unaffected by phosphate, citrate, and F- and by Na+ and K+; NH4+ is partially inhibitory. The enzyme is also sensitive to iodoacetic acid. It is generally more similar to yeast N alpha-acetyltransferase Lee, F.-J. S., Lin, L.-W., & Smith, J. A. (1988) J. Biol. Chem. 263, 14948-14955] than to the hen oviduct enzyme, which contains a 7S RNA subunit Kamitani, K., & Sakiyama, F. (1989) J. Biol. Chem. 264, 13194-13198], although the amino acid compositions are quite different.