ABSTRACT
Ribulose-1,5-bisphosphate carboxylase-oxygenase is one of the most abundant proteins in the biosphere. The amount present in leaf tissue varies, of course, with nutrient levels and plant species, but is of the order of 6 mg per mg chlorophyll. Ribulose-1,5-bisphosphate carboxylase-oxygenase serves as a major form of storage of organic nitrogen in the plant. Activation and deactivation of ribulose-1,5-bisphosphate carboxylase are physiological phenomena in isolated chloroplasts and protoplasts. The degree of activation may be assayed by hypotonic or surfactant lysis of the membranes in a carboxylase-oxygenase assay medium. Ribulose-1,5-bisphosphate carboxylase-oxygenase in C-3 plants is clearly a yield-limiting factor of major importance in agriculture. Photosynthesis in C-3 plants increased when ambient CO2 was increased at high light intensities. The increased photosynthate availability should increase vegetative growth and the rate of leaf area expansion.
