Mammalian cells contain a number of enzymes catalyzing the acetylation of polyamines and histones including an inducible spermidine/spermine N′-acetyltransferase which may play a key role in regulating the interconversion of polyamines [Matsui, I., Wiegand, L., & Pegg, A. E. (1981) J. Biol. Chem. 256, 2454-2459]. The present experiments were carried out in order to provide a method to distinguish this enzyme from other polyamine/histone acetylases and to test whether specific inhibitors of its activity could be obtained. Rabbit antiserum to homogeneous rat liver spermidine/spermine N′-acetyltransferase had no effect on the activity of a crude nuclear extract from rat liver, indicating that its spermidine acetylating capability is not related to the cytosolic spermidine/spermine N1-acetyltransferase induced by hepa-totoxins. Potential multisubstrate analogues were prepared by attaching various polyamines to coenzyme A via an acetic acid linkage and tested as potential inhibitors of the acetylation of spermidine and histones. There was little difference in the potency of these polyamine derivatives as inhibitors of histone or spermidine acetylation by the crude nuclear extracts which appeared to contain at least two such activities, one inhibited completely by 20-30 - and the other amounting to 50% of the total being unaffected by 100 -. Spermidine/spermine N-acetyltransferase was also inhibited by all the derivatives, but the potency toward this enzyme differed widely. The derivative from symnorspermidine was a very strong inhibitor, giving 50% inhibition at 0.3 -, and was more than 1 order of magnitude more active than the others. These results are consistent with TV- [2-(5′-coenzyme A)acetyl] -sym-norspermidine amide acting as a multisubstrate analogue since symnorspermidine is a preferred substrate of spermidine/spermine N-acetyltransferase, having a Km (9μM) 14 times less than that for spermidine (130 -). Comparisons of the effects of these inhibitors on cells and nuclear extracts may be valuable in understanding the physiological role of polyamine and histone acetylases.
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