A spectrophotometric procedure for assay of initial and total activity of ribulose 1,5-bisphosphate carboxylase in maize leaves was established. The extraction of the crude enzyme from maize leaf tissue, which was prefrozen in liquid nitrogen, desalting of the extract, and assay of the enzyme was completed within 3 min. From experiments adding deactivated ribulose 1,5-bisphosphate carboxylase to the leaf tissue prior to extraction it was estimated that the maximum extent of activation during extraction, desalting and assay was 8%. In predarkened leaves the enzyme showed 67 to 84%of maximal activation while in preilluminated leaves the enzyme showed 89 to 98%of maximal activation. These results indicate that deactivation of the enzyme in the dark is not a reason for the previous finding of a transient peak of ribulose 1,5-bisphosphate in maize leaves during induction of photosynthesis [Usuda (1985)Plant Physiol. 78: 859–864]. This transient increase in the substrate level upon illumination might be explained by the presence of an unknown negative effector for ribulose 1,5-bisphosphate carboxylase in vivo in leaf tissue in the dark, or limiting CO2supply to the enzyme during the induction perio
展开▼
