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Multiple Reaction Products from the Hydrolysis of Chiral and Pro-chiral Organophosphate Substrates by the Phosphotri-esterase from Sphingobium sp. TCM1
The phosphotriesterase from
Sphingobium
sp. TCM1 (
Sb
-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
Sb
-PTE for hydrolysis of chiral phosphotriesters we discovered that multiple phosphodiester products are formed from a single substrate. For example,
Sb
-PTE catalyzes the hydrolysis of the (
R
P
)-enantiomer of methyl cyclohexyl
p
-nitrophenyl phosphate with exclusive formation of methyl cyclohexyl phosphate. However, the enzyme catalyzes hydrolysis of the (
S
P
)-enantiomer of this substrate to an equal mixture of methyl cyclohexyl phosphate and cyclohexyl
p
-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
p
-nitrophenyl ester contained within the same substrate is remark-able. The overall scope of the stereoselective properties of this enzyme is addressed with a library of chiral and prochiral substrates.