The Activation State of Ribulose 1,5-bisphosphate Carboxylase in Maize Leaves in Dark and Light

A spectrophotometric procedure for assay of initial and totalactivity of ribulose 1,5-bisphosphate carboxylase in maize leaveswas established. The extraction of the crude enzyme from maizeleaf tissue, which was prefrozen in liquid nitrogen, desaltingof the extract, and assay of the enzyme was completed within3 min. From experiments adding deactivated ribulose 1,5-bisphosphatecarboxylase to the leaf tissue prior to extraction it was estimatedthat the maximum extent of activation during extraction, desaltingand assay was 8%. In predarkened leaves the enzyme showed 67to 84% of maximal activation while in preilluminated leavesthe enzyme showed 89 to 98% of maximal activation. These resultsindicate that deactivation of the enzyme in the dark is nota reason for the previous finding of a transient peak of ribulose1,5-bisphosphate in maize leaves during induction of photosynthesis[Usuda (1985) Plant Physiol. 78: 859–864]. This transientincrease in the substrate level upon illumination might be explainedby the presence of an unknown negative effector for ribulose1,5-bisphosphate carboxylase in vivo in leaf tissue in the dark,or limiting CO₂ supply to the enzyme during the induction period. (Received May 30, 1985; Accepted August 16, 1985)