QUANTITATIVE-DETERMINATION OF RUBP CARBOXYLASE-OXYGENASE PROTEIN IN LEAVES OF SEVERAL C-3 AND C-4 PLANTS

RuBP carboxylase-oxygenase protein in three C3 species (Nicotiana tabacum L., Solanum tuberosum L., Triticum aestivum L.) and three C4 species (Panicum miliaceum L., Panicum texanum Buckl., Zea mays L.) was quantitatively determined by sucrose density gradient centrifugation and by immunochemical assay using antibody raised to crystallized tobacco leaf RuBP carboxylase-oxygenase. The C3 species had 3- to 6-fold higher concentrations of RuBP carboxylase-oxygenase than the C4 species when expressed on either a chlorophyll or a leaf area basis. The C3 species also allocated a higher fraction of their total soluble protein to this enzyme (from 25 to 60% for the C3 species compared to 8 to 23% for the C4 species). There was no RuBP carboxylase-oxygenase protein or activity in the C4 mesophyll cells, while the enzyme constituted from 20 to 40% of the total soluble protein in the C4 bundle sheath cells. A close correlation (r = +0·91) was found between catalytic activity and level of the enzyme protein in the species examined. © 1979 Oxford University Press.