A new ether bond-splitting enzyme found in Gram-positive polyethylene glycol 6000-utilizing bacterium, Pseudonocardia sp. strain K1

Pseudonocardia sp. strain K1 is the only Gram-positive bacterium among the bacteria aerobically metabolizing polyethylene glycol (PEG). Generally, PEG is metabolized by an oxidative pathway in which a terminal alcohol group of PEG is oxidized to aldehyde and to carboxylic acid and then an ether bond is oxidatively cleaved. As the cell-free extract of Pseudonocardia sp. strain K1 has PEG dehydrogenase, PEG aldehyde dehydrogenase and diglycolic acid (DGA) dehydrogenase (DGADH) activities, all of which are constitutively formed, the strain has a metabolic pathway similar to that so far known. We purified an ether bond-splitting enzyme as DGADH. The molecular mass of the enzyme was estimated to be 55 kDa; and it consisted of two identical subunits. The enzyme oxidatively cleaved both an ether bond of PEG 3000 dicarboxylic acid and DGA. The N-terminal amino acid sequence of the purified enzyme had high homology with various superoxide dismutases and the enzyme had also superoxide dismutase activity. The atomic absorption spectrum showed that approximately one atom of Fe was included in each subunit of the enzyme. DGADH activity increased in the cells grown in a PEG medium supplemented with FeCl₃. Thus, we concluded that the enzyme purified from Pseudonocardia sp. strain K1 is a new ether bond-splitting enzyme.