The Activation of Ribulose-l,5-bisphosphate Carboxylase-Oxygenase from Spinach by Oxygen Changes of the Enzyme Conformation during Air-Argon Transitions

Ribulose-l,5-bisphosphate Carboxylase, Ribulose-l,5-bisphosphate Oxygenase, Enzyme Confor­ mation, Oxygen Effect, Photosynthesis The effect of oxygen on ribulose-l,5-bisphosphate carboxylase-oxygenase from spinach was in­ vestigated. Both activities were deactivated by removal of oxygen and reversibly reactivated by oxygenation of the enzyme solution. The change in enzyme activities was accompanied by confor­ mational changes as studied by the use of intrinsic and extrinsic fluorescent probes. The analysis of cysteine sulfhydryl groups accessible to 5,5'-dithiobis-(2-nitrobenzoic acid) re­ vealed that the number of these groups changed with the oxygen concentration. The kinetic of the exposure of eight cysteine residues was similar to the loss of enzyme activities. The modification of these groups with 5,5'-dithiobis-(2-nitrobenzoic acid) caused almost complete loss of both the activities. The enzyme isolated from a photolithotrophic organism, Chromatium vinosum, was not affected by oxygen removal. During air — argon transitions, neither the enzyme conformation nor the num­ ber of accessible sulfhydryl groups changed.