Identification of paraoxonase 3 in rat liver microsomes: purification and biochemical properties

Three paraoxonase genes (PON1, PON2 and PON3) have been described so far in mammals. Although considerable information is available regarding PON1, little is known about PON2 and PON3. PON3 has been isolated recently from rabbit serum [Draganov, Stetson, Watson, Billecke and La Du (2000) J. Biol. Chem. 275, 33435-33442] and liver [Ozols (1999) Biochem. J. 338, 265-275]. In the present study, we have identified the presence of PON3 in rat liver microsomes and a method for the purification to homogeneity is presented. PON3 has been purified 177-fold to apparent homogeneity with a final specific activity of 461 units/mg using a method consisting of seven steps: solubilization of the microsomal fraction, hydroxyapatite adsorption, chromatography on DEAE-Sepharose CL-6B, non-specific affinity chromatography on Cibacron Blue 3GA, two DEAE-cellulose steps and a final affinity chromatography on concanavalin A-Sepharose. SDS/PAGE of the final preparation indicated a single protein-staining band with an apparent molecular mass of 43 kDa. The isolated protein was identified by nanoelectrospray MS. Internal amino acid sequences of several peptides were determined and compared with those of human, rabbit and mouse PON3, showing a high similarity. Some biochemical properties of PON3 were also studied, including optimum pH, K(m) and heat and pH stability.

Cell Surface Display of Organophosphorus Hydrolase in Pseudomonas putida Using an Ice-Nucleation Protein Anchor

A surface anchor system derived from the ice-nucleation protein (INP) from Pseudomonas syringe was used to localize organophosphorus hydrolase (OPH) onto the surface of Pseudomonas putida KT2440. Cells harboring the shuttle vector pPNCO33 coding for the INP-OPH fusion were capable of targeting OPH onto the cell surface as demonstrated by whole cell ELISA. The whole cell activity of P. putida KT2440 was shown to be 10 times higher than those of previous efforts expressing the same fusion protein in Escherichia coli. The capability of expressing enzymes on the surface of a robust and environmentally benign P. putida KT2440 should open up new avenues for a wide range of applications such as in situ bioremediation.

Langmuir and Langmuir-Blodgett films of organophosphorus acid anhydrolase

In this paper, we describe the preparation and characterization of Langmuir and Langmuir-Blodgett (LB) monolayers of the enzyme organophosphorus acid anhydrolase (OPAA). Langmuir films of OPAA were characterized on different subphases, such as phosphate, ammonium carbonate, and bis-tris-propane buffers. Monolayers at the air-water interface were characterized by measuring the surface pressure and surface potential-area isotherms. In situ UV-vis absorption spectra were also recorded from the Langmuir monolayers. The enzyme activity at the air-water interface was tested by the addition of diisopropylfluorophosphate (DFP) to the subphase. LB films of OPAA were transferred to mica substrates to be studied by atomic force microscopy. Finally, a one-layer LB film of OPAA labeled with a fluorescent probe, fluorescein isothiocyanate (FITC), was deposited onto a quartz slide to be tested as sensor for DFP. The clear, pronounced response and the stability of the LB film as a DFP sensor show the potential of this system as a biosensor.

Structure-activity relationship on human serum paraoxonase (PON1) using substrate analogues and inhibitors

Substrate analogues based on the parent compounds paraoxon and phenyl acetate were tested on human serum paraoxonase (PON1) to explore the active site of the enzyme. Replacement of the nitro group of paraoxon with an amine or hydrogen, as well as electronic changes to the parent compound, converted these analogues into inhibitors. Introduction of either electron-withdrawing or donating groups onto phenyl acetate resulted in reduction in their rate of hydrolysis by PON1.