Multiple Reaction Products from the Hydrolysis of Chiral and Prochiral Organophosphate Substrates by the Phosphotriesterase from <i>Sphingobium</i> sp. TCM1

The phosphotriesterase from <i>Sphingobium</i> sp. TCM1 (<i>Sb</i>-PTE) is notable for its ability to hydrolyze organophosphates that are not substrates for other enzymes. In an attempt to determine the catalytic properties of <i>Sb</i>-PTE for hydrolysis of chiral phosphotriesters, we discovered that multiple phosphodiester products are formed from a single substrate. For example, <i>Sb</i>-PTE catalyzes the hydrolysis of the <i>R</i><sub>P</sub>-enantiomer of methyl cyclohexyl <i>p</i>-nitrophenyl phosphate with exclusive formation of methyl cyclohexyl phosphate. However, the enzyme catalyzes hydrolysis of the <i>S</i><sub>P</sub>-enantiomer of this substrate to an equal mixture of methyl cyclohexyl phosphate and cyclohexyl <i>p</i>-nitrophenyl phosphate products. The ability of this enzyme to catalyze the hydrolysis of a methyl ester at the same rate as the hydrolysis of a <i>p</i>-nitrophenyl ester contained within the same substrate is remarkable. The overall scope of the stereoselective properties of this enzyme is addressed with a library of chiral and prochiral substrates.