Plant Physiol. Drug Metab Dispos
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Plant Physiology 77:735-739 (1985)
© 1985 American Society of Plant Biologists

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Articles

Ribulose Bisphosphate Carboxylase/Oxygenase Content Determined with [14C]Carboxypentitol Bisphosphate in Plants and Algae 1

Akiho Yokota2 and David T. Canvin

Department of Biology, Queen's University, Kingston, Ontario, Canada K7L 3N6

As is the case with spinach ribulose bisphosphate carboxylase/oxygenase (Rubisco), [14C]carboxyarabinitol bisphosphate (CABP) bound to purified Chlorella Rubisco with a molar ratio of unity to large subunit of the enzyme. The concentration of binding sites in extracts of photosynthetic organisms was determined by reacting the extracts with [14C]-carboxypentitol bisphosphate (CPBP) and precipitating the resultant Rubisco-[14C]CABP complex with a combination of polyethylene glycol-4000 and MgCl2. Plots of the relationship between concentrations of [14C] CPBP in the reaction mixture and the precipitated [14C]CPBP gave a straight line and the concentration of binding sites were estimated by extrapolation to zero [14C]CPBP since the dissociation constant of CABP with Rubisco is 10–11 molar. Spinach, pea, and soybean leaves contained 6.4 to 6.8 milligrams Rubisco per milligram chlorophyll, corresponding to 92 to 97 ribulose bisphosphate-binding sites per milligram chlorophyll. The Rubisco content of sunflower and wheat leaves was 5.3 to 5.5 milligrams per milligram chlorophyll. The concentrations in C4 plants were not uniform and corn and Panicum miliaceum leaves contained 3 and 7 milligrams Rubisco per milligram chlorophyll. The Rubisco content of green algae was one-fifth to one-sixth that of C3 plant leaves and was affected by the CO2 concentration during growth. The content of Euglena and blue-green algae is also reported.

2 Present address: Department of Agricultural Chemistry, University of Osaka Prefecture, Sakai, Osaka 591, Japan.

1 Supported by the Natural Sciences and Engineering Research Council of Canada.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1985 by the American Society of Plant Biologists