Kinetic properties of the purified 3-hexulosephosphate synthase from Pseudomonas oleovorans

The kinetic characteristics of the purified 3-hexulosephosphate synthase from the facultative methylotroph Pseudomonas oleovorans were investigated. It could be demonstrated that the dependence of the reaction rate on the rib(ul)ose-5-phosphate as well as the formaldehyde concentration has a complex shape with the appearence of plateau and trough regions. The shape of the curve is changed in dependence on the fixed level of the second substrate. Multiple forms of the 3-hexulosephosphate synthase were found to be responsible for the generation of the complex kinetic characteristics. By means of ion exchange chromatography it was possible to separate four active enzyme forms with different kinetic characteristics. These forms were also found to be interconvertible. This behaviour of the 3-hexulosephosphate synthase is assumed to have the main regulatory function of the enzyme.