Purification and characterization of spermidine N1‐acetyltransferase from chick duodenum

We have reported that spermidine N1‐acetyltransferase has a larger role than ornithine decarboxylase in putrescine synthesis in chick duodenum induced by 1α,25‐dihydroxycholecalciferol (calcitriol) [Shinki, T., Kadofuku, T., Sato, T. and Suda, T. (1986) J. Biol. Chem. 261, 11 712–11 716]. In the present study, spermidine N1‐acetyltransferase was purified from the duodenal cytosol of calcitriol‐treated chicks to homogeneity judged by SDS/polyacrylamide gel electrophoresis. The purified enzyme converted spermidine only to N1‐acetylspermidine. The apparent molecular mass of the purified spermidine N1‐acetyltransferase was found to be 36 kDa by gel filtration on Sephacryl S‐200 and 18 kDa by SDS polyacrylamide gel electrophoresis. When duodenal crude 105000 x g extracts were directly applied to a Sephacryl S‐200 column without prior purification, three peaks with spermidine N1‐acetyltransferase activity appeared. The first peak was in the void volume, the second peak was in the fraction corresponding to an apparent molecular mass of 70 kDa, and the third peak was in the fraction corresponding to 36 kDa. These results suggest that spermidine N1‐acetyltransferase exists as a dimer of the 18 kDa subunits and is stabilized in (a) form(s) bound to other components or proteins in intact cells.