3,4-Dihydroxyphenylacetate 2,3-dioxygenase from Klebsiella pneumoniae, a Mg2+-containing dioxygenase involved in aromatic catabolism

3,4-Dihydroxyphenylacetate 2,3-dioxygenase, an extradiol-ring-cleavage dioxygenase, has been purified from Klebsiella pneumoniae to homogeneity. The enzyme has an M(r) of 102,000 in its tetrameric form with an M(r) of 25,500 for each subunit. Unlike most other dioxygenases, the enzyme reported here contains Mg2+, as determined by atomic-absorption spectrophotometry and plasma emission metal analysis. The enzyme was shown to contain approx. 1 g-atom of Mg2+/mol of protein and we suggest an alpha 4 Mg2+ quaternary structure. This is the first report of a dioxygenase containing Mg2+ in its structure.