Abstract: | RuBP carboxylase-oxygenase protein in three C3 species (Nicotianatabacum L., Solanum tuberosum L., Triticum aestivum L.) andthree C4 species (Panicum miliaceum L., Panicum texanum Buckl.,Zea mays L.) was quantitatively determined by sucrose densitygradient centrifugation and by immunochemical assay using antibodyraised to crystallized tobacco leaf RuBP carboxylase-oxygenase.The C3 species had 3- to 6-fold higher concentrations of RuBPcarboxylase-oxygenase than the C4 species when expressed oneither a chlorophyll or a leaf area basis. The C3 species alsoallocated a higher fraction of their total soluble protein tothis enzyme (from 25 to 60% for the C3 species compared to 8to 23% for the C4 species). There was no RuBP carboxylase-oxygenaseprotein or activity in the C4 mesophyll cells, while the enzymeconstituted from 20 to 40% of the total soluble protein in theC4 bundle sheath cells. A close correlation (r = +0·91)was found between catalytic activity and level of the enzymeprotein in the species examined. |