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 g ene, Bit, which encodes a multidrug export protein whose overexpression fac ilitates spermidine export [Woolridge, Vazquez-Laslop, Markham, Chevalier, Gerner and Neyfakh (1997) J. Biol. Chem. 272, 8864-8866]. Here we show that BltD acetylates both spermidine and spermine at primary propyl amine moiet ies, with spermine being the preferred substrate. In the presence of satura ting concentrations of acetyl CoA, BltD rapidly acetylates spermine at both the N-1 and N-12 positions. The K-m (app) values for spermine, spermidine and N-1-acetylspermine are less than or equal to 67, 200 and 1200 mu M, res pectively. Diamines ranging from 1,3-diaminopropane to 1,12-diaminododecane , monoacetylputrescine and N-8-acetylspermidine were not substrates for Blt D. Putrescine (1,4-diaminobutane) and N-8-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 acet yl-CoA interactions with BltD. These data and other results indicate that t he mechanism of spermidine and spermine acetylation by BltD is a random-ord er mechanism of bi-molecular kinetics.