Small Angle X-Ray Study on the Structure of Active and Inactive Ribulose-l,5-bisphosphate Carboxylase-Oxygenase from Spinach. Evidence for a Configurational Change

Small angle X -ray scattering studies on ribu lose-l,5 -b isphosphate carboxylase-oxygenase (R ubisco) from spinach reveal a configurational change in its quaternary structure upon the transition of the m olecule from the activated form occurring in the presence of C 0 2 and Mg2+ to the deactivated form ob tained w hen C 0 2 and M g2+ are rem oved by extensive dialysis under n itrogen. Present structural m odels are com parable to m odels which were postu lated previously for the same enzym e but isolated from the hydrogen bacterium Alcaligenes eutrophus [O. M eisenberger, I. Pilz, B. B ow ien, G . P. Pal, and W. Saenger, J. Biol. Chem. 259, 4463—4465 (1984)]. T he radius of gyration is R = 47.5 ± 0 .2 nm for the active spinach Rubisco. Upon deactivation , R changes to 49.2 ± 0 .2 nm , suggesting a m ore elongated quaternary structure. The observed differ­ ence in deactivation behaviour in am bient and in n itrogen a tm osphere indicates a higher affinity of this spinach enzym e to C 0 2 with respect to the sam e enzyme from Alcaligenes eutrophus.