The Biotransformation of Propylene to Propylene Oxide by Methylococcus Capsulatus (Bath): 2. A Study of the Biocatalyst Stability

Methylococcus capsulatus (Bath) possesses methane monooxygenase (MMO) which catalyses the epoxidation of propylene to propylene oxide. MMO activity could be maintained in whole cells by storage in unagitated vessels for several days. However if these cells were agitated and aerated in the absence of a carbon and energy source then 80% of the propylene-oxidizing activity Was lost within 24 h. It was shown that this loss of activity was due to the inability of the cells to provide energy to drive the oxidation process rather than the loss of MMO activity per se. If propylene oxide was added to these aerated cells then the rate of inactivation was increased and 50% of the activity was lost over a 10 min period. The addition of an exogenous energy source caused a doubling in the rate of inactivation. These marked increases in the rates of inactivation in the presence of propylene oxide were found to be caused by the loss of the methane monooxygenase activity per se rather than a further loss of the energy-producing systems. Cells actively producing propylene oxide from propylene, using methanol as an energy source, also lost their propylene oxide-producing capacity rapidly due to loss of the methane monooxygenase activity. The rate of inactivation under these circumstances was related to the rate of propylene oxide production from propylene rather than the level of this product in the culture supernatant.