Cellular homeostasis is dependent on the structural and functional integrity of the cell's membrane lipid bilayer.As such, processes that damage the membrane can interfere with signal transduction, molecular recognition and transport, maintenance of membrane potential, or cellular metabolism and thus have the potential to initiate disease.'Abbreviations: LOO*, lipid peroxyl radical (initiating); LH, lipid; LOOH, lipid hydroperoxide (generic); LOO', lipid peroxyl radical; HO*, hydroxyl radical; 13-LOOH, 13-hydroperoxylinoleic acid; EDTA, ethylenediaminetetraacetic acid; HOO', perhydroxyl (hydrodioxyl) radical; XO, xanthine oxidase; N-HT, N-hydroxy-2-thiopyridone; ROO*, peroxyl radical (generic); R*, carbon-centered radical (generic); R0', alkoxyl radiad (generic); ROOH, hydroperoxide (generic); LO*, lipid peroxyl radical (generic); NOs, nitrogen dioxide; NO*, nitrous oxide; ONOO", peroxynitrite; RS', thiyl radical (generic); RSH, thiol (generic); SO3, sulfite radical anion; ' ,02, singlet oxygen; SOD, superoxide dismutase; LUV, large unilamellar vesicle.

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A new enzyme homologous to phosphotriesterase was identified from the bacterium Geobacillus stearothermophilus (GsP). This enzyme belongs to the amidohydrolase family and possesses the ability to hydrolyze both lactone and organophosphate (OP) compounds, making it a phosphotriesterase-like lactonase (PLL). GsP possesses higher OP-degrading activity than recently characterized PLLs, and it is extremely thermostable. GsP is active up to 100°C with an energy of activation of 8.0 kcal/mol towards ethyl paraoxon, and it can withstand an incubation temperature of 60°C for two days. In an attempt to understand the thermostability of PLLs, the X-ray structure of GsP was determined and compared to those of existing PLLs. Based upon a comparative analysis, a new thermal advantage score and plot was developed and reveals that a number of different factors contribute to the thermostability of PLLs.

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