Characterization of putative tryptophan monooxygenase from Ralstonia solanasearum

The amino-acid sequence of a putative tryptophan monooxygenase (PTMO) from Ralstonia solanacearum is homologous with that of proenzyme (proPAO) of L -Phe oxidase (deaminating and decarboxylating) (PAO) from Pseudomonas sp. P-501 in their overall sequences. PTMO was expressed in E. coli and purified, but had no catalytic activity to oxidize L -Phe. By treating PTMO with various proteases, the Pronase-treated PTMO (PTMOp) showed a relatively high activity to oxidize L -Phe, L -Trp, L -Tyr and L -Met. Studies on the stoichiometry of the reaction showed that L -Phe and L -Tyr were mostly oxygenated, that L -Met was mostly oxidized, and both oxygenation and oxidation of L -Trp was observed. Initial velocity patterns were a ping-pong type with L -Phe and L -Tyr, and a sequential type with L -Trp and L -Met as substrate. The spectrum of enzymes with sufficient amounts of these substrates to reduce the enzyme showed a long wavelength species (purple complex) with L -Phe, but not with L -Tyr, L -Trp and L -Met. These results lead to the conclusion that PTMO and PTMOp belong to proPAO and PAO, respectively.