Small Angle X-Ray Study on the Structure of Active and Inactive Ribulose-1,5-bisphosphate Carboxylase-Oxygenase from Spinach. Evidence for a Configurational Change

Abstract

Small angle X-ray scattering studies on ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) from spinach reveal a configurational change in its quaternary structure upon the transition of the molecule from the activated form occurring in the presence of CO2 and Mg2+ to the deactivated form obtained when CO2 and Mg2+ are removed by extensive dialysis under nitrogen. Present structural models are comparable to models which were postulated previously for the same enzyme but isolated from the hydrogen bacterium Alcaligenes eutrophus [O. Meisen- berger, I. Pilz, B. Bowien, G. P. Pal, and W. Saenger, J. Biol. Chem. 259, 4463-4465 (1984)]. The 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 more elongated quaternary structure. The observed differ­ence in deactivation behaviour in ambient and in nitrogen atmosphere indicates a higher affinity of this spinach enzyme to CO2 with respect to the same enzyme from Alcaligenes eutrophus.