Characterization of a novel spermidine/spermine acetyltransferase, BltD, from Bacillus subtilis

Overexpression of the BltD gene in Bacillus subtilis causes acetylation of the polyamines spermidine and spermine. BltD is co-regulated with another gene, Blt, which encodes a multidrug export protein whose overexpression facilitates spermidine export. Here we show that BltD acetylates both spermidine and spermine at primary propyl amine moieties, with spermine being the preferred substrate. In the presence of saturating concentrations of acetyl CoA, BltD rapidly acetylates spermine at both the N¹ and N¹2 positions. The K(m) (app) values for spermine, spermidine and N¹-acetylspermine are ≤ 67, 200 and 1200 μM, respectively. Diamines ranging from 1,3-diaminopropane to 1,12-diaminododecane, monoacetylputrescine and N⁸-acetylspermidine were not substrates for BltD. Putrescine (1,4-diaminobutane) and N⁸-acetylspermidine were competitive inhibitors of spermidine acetylation by BltD, with K(i) values of 0.25 and 5.76 mM, respectively. CoA competitively inhibited both spermidine and acetyl-CoA interactions with BltD. These data and other results indicate that the mechanism of spermidine and spermine acetylation by BltD is a random-order mechanism of bi-molecular kinetics.