Partial purification and characterization of polyethylene glycol/polylene glycol-degrading enzymes from Pseudomonas sp. PE-2

Abstract

Polyethylene glycol (PEG) and polypropylene glycol (PPG) have been widely used as raw materials for many industries. Consequently, they are released into wastewater system and environment. Their biodegradation have been studied in Pseudomonas sp. PE-2. Polyethylene glycol dehydrogenase (PEG-DH) and polypropylene glycol dehydrogenase (PPG-DH) activities were found in cell-free extract of Pseudomonas sp. PE-2. Both enzymes were inducible when PEGs and PPGs served as a sole carbon and energy sources. In the late phase of logarithmic growth, most of the PEG-DH activities (76.6%) were found in the periplasm, while PPG-DH activities (82%) were in the cytoplasm. The PEG-DH and PPG-DH in cell-free extract were partially purified by ammonium sulfate precipitation, anion-exchange column and hydrophobic column to 11.8 and 51.4 fold, respectively. The partially purified PEG-DH is a monomer of 73.6 kDa. PPG-DH appeared to consist of two identical subunits of 36 kDa. The optimum pH and temperature of the PEG-DH and PPG-DH were at pH 9.0, 25°C and pH 7.5, 25°C, respectively. The partially purified PEG-DH and PPG-DH were stable in the pH range of 8.0 to 9.5 and 7.0 to 8.0, respectively. Moreover, both enzymes were stable below 30°C and had pyrroloquinoline quinone (PQQ) as cofactor. The metal ions at 2 mM inhibited the PEG-DH and PPG-DH activities by 8-100% and 5-30%, respectively, while Ni²⁺ could enhance the PPG-DH activity by 38%. The enzymes oxidized various kinds of PEGs and PPGs, among which, PEG 600 and PPG 725 were the most active substrates for PEG-DH and PPG-DH, respectively. The apparent K[subscript m] values of PEG-DH for PEG 600, PEG 2000, PEG 4000, PEG 6000 and PEG 8000 were 0.7, 3.3, 4.6, 30.5 and 28.3 mM, respectively, whereas those of PPG-DH for PPG 725, PPG 1000 and PPG 2000 were 5.1, 4.6 and 12.6 mM, respectively.