An enzyme catalyzing the acetylation of the polyamines, spermidine or spermine, has been purified 112000-fold to homogeneity from livers of rats treated with carbon tetrachloride. Major purification steps involved affinity chromatography on sym-norspermidine-Sepharose, from which the enzyme was eluted by spermidine, and affinity chromatography on Cibacron blue agarose, from which the enzyme was released by coenzyme A. Similar final specific activities were obtained by using either method as a final purification step, providing strong evidence for homogeneity. The enzyme preparation gave a single band on Polyacrylamide gel electrophoresis carried out under native or denaturing conditions. It had an apparent molecular weight of about 115 000 made up of two subunits of 60000. The acetyltransferase acted on spermidine to form only N1-acetylspermidine. Spermine was also a substrate, giving N1-acetylspermine, and N1-acetylspermine could be acetylated to form N1,N12-diacetylspermine. The Vmax values for spermidine, spermine, and N1-acetylspermine were 8, 1.8, and 1.2 µmol of product min−1 mg−1, respectively, when assays were carried out in the presence of saturating concentrations of acetyl-CoA. The Km for acetyl-CoA was 1.5 µM. and the for spermidine, spermine, and N1-acetylspermine were 130 µM, 35 µM, and 30 µM, respectively. These results suggest that both spermidine and spermine would be physiological substrates for this enzyme. Coenzyme A was quite strongly inhibitory, having a Ki of 40 µM, but an even more powerful inhibitor could be produced by reacting coenzyme A with methyl methanethiosulfate to form coenzyme A methyl disulfide. The purified enzyme had no deacetylase activity and the reaction was effectively irreversible. The name spermidine/spermine N1-acetyltransferase is suggested for this enzyme, which may play an important role in the interconversion of polyamines.
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