Enzymatic Characterization of 5-Methylthioribulose-1-phosphate Dehydratase of the Methionine Salvage Pathway in Bacillus subtilis

抄録

5-Methylthioribulose-1-phosphate (MTRu-1-P) dehydratase catalyzes the reaction from MTRu-1-P to 2,3-diketo-5-methylthiopentyl-1-phosphate (DK-MTP-1-P) in the methionine salvage pathway in Bacillus subtilis. The properties of this enzyme remain to be determined. We characterized these properties using a recombinant protein. The enzyme, with a molecular mass of 90 kDa, was composed of four subunits. The K_m and V_max of the enzyme were 8.9 μM and 42.7 μmole min⁻¹ mg protein⁻¹ at 25 °C respectively. Maximum activity was observed at pH 7.5 to 8.5 and 40 °C. The activation energy of the reaction from MTRu-1-P to DK-MTP-1-P was 63.5 kJ mol⁻¹. The reaction product DK-MTP-1-P was labile, and decomposed at a rate constant of 0.048 s⁻¹ to an unknown compound that was not utilized by DK-MTP-1-P enolase, the enzyme catalyzing the next step. The function of this enzyme in the pathway is discussed.