Molecular and catalytic properties of 2,4'-dihydroxyacetophenone dioxygenase from Burkholderia sp. AZ11.

The gene dad encoding 2,4'-dihydroxyacetophenone (DHAP) dioxygenase was cloned from Burkholderia sp. AZ11. The initiation codon GTG was converted to ATG for high-level expression of the enzyme in Escherichia coli. The enzyme was moderately thermostable, and the recombinant enzyme was briefly purified. The enzyme (M(r)=90 kDa) was a homotetramer with a subunit M(r) of 23 kDa. It contained 1.69 mol of non-heme iron, and had a dark gray color. On anaerobic incubation of it with DHAP, the absorption at around 400 nm increased due to the formation of an enzyme-DHAP complex. Multiple sequence alignment suggested that His77, His79, His115, and Glu96 in the cupin fold were possible metal ligands. The apparent K(m) for DHAP and the apparent V(max) were estimated to be 1.60 µM and 6.28 µmol/min/mg respectively. 2-Hydroxyacetophenone was a poor substrate. CuCl(2) and HgCl(2) strongly inhibited the enzyme, while FeSO(4) weakly activated it.