Reversible inactivation and characterization of purified inactivated form I ribulose 1,5-bisphosphate carboxylase/oxygenase of Rhodobacter sphaeroides.

Form I ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) from Rhodobacter sphaeroides is inactivated upon the addition of organic acids to photolithoautotrophically grown cultures. Activity recovers after the dissipation of the organic acid from the culture. The inactivation process depends on both the concentration of the organic compound and the nitrogen status of the cells. The inactivated RubisCO has been purified and was shown to exhibit mobility on both nondenaturing and sodium dodecyl sulfate gels different from that of the active enzyme prepared from cells not treated with organic acids. However, the Michaelis constants for ribulose 1,5-bisphosphate and CO2 or O2 were not dramatically altered. Purified inactivated RubisCO could be activated in vitro by increasing the temperature or the levels of Mg(II), and this activation was accompanied by changes in the electrophoretic mobility of the protein. When foreign bacterial RubisCO genes were expressed in an R. sphaeroides host strain lacking the ability to synthesize endogenous RubisCO, only slight inactivation of RubisCO activity was attained.