Multiplicity of 3-hexulosephosphate synthase from bacterium MB 58. 2. Generation of complex kinetic characteristics

3-hexulosephosphate synthase (HPS) from the facultative methanol-utilizing Bacterium MB 58 exhibits a complex kinetic behaviour characterized by intermediary plateau regions. This feature could be related to the existence of multiple enzyme forms. With the aid of gel chromatography or isoelectric focusing purified HPS has partially been separated into at least four fractions. The individual enzyme forms are characterized by different kinetic properties exhibiting either hyperbolic or sigmoidal response to substrate saturation. In the sum of their action these forms generate the complex shape of the kinetic characteristics. Furthermore, these forms were found to be interconvertible. After partial separation a new equilibrium between the conformers is established in each case. The multiplicity of HPS can be demonstrated in qualitatively the same manner with the purified enzyme and with freshly prepared crude extracts. Proteolytic modifications on the enzyme as a cause for the multiplicity could be ruled out. The multiple character of the enzyme is also evident at different pH-values showing two optima. At different temperatures, anomalies in the Arrhenius plot depending on the substrate concentration were observed. From the present data a qualitative model of regulating HPS in the methylotrophic metabolism is proposed. Accordingly, several stable states of the metabolism should be realized.