Putative ACP phosphodiesterase gene (acpD) encodes an azoreductase

An FMN-dependent NADH-azoreductase of Escherichia coli was purified and ana lyzed for identification of the gene responsible for azo reduction by micro organisms. The N-terminal sequence of the azoreductase conformed to that of the acpD gene product, acyl carrier protein phosphodiesterase. Overexpress ion of the acpD gene provided the E. coli with a large amount of the 23-kDa protein and more than 800 times higher azoreductase activity. The purified gene product exhibited activity corresponding to that of the native azored uctase. The reaction followed a ping-pong mechanism requiring 2 mol of NADH to reduce I mol of methyl red (4 ' -dimethylaminoazobenzene-2-carboxylic a cid) into 2-aminobenzoic acid and N,N ' -dimethyl-p-phenylenediamine. On th e other hand, the gene product could not convert holo-acyl carrier protein into the apo form under either in vitro or in vivo conditions. These data i ndicate that the acpD gene product is not acyl carrier protein phosphodiest erase but an azoreductase.