Quantitative Determination of RuBP Carboxylase–Oxygenase Protein in Leaves of Several C3and C4Plants

Abstract

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.