PLANT PHYSIOLOGY , Vol 111, Issue 2 441-445, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Isolation of a Protein Containing Covalently Linked Large and Small Subunits of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase from Botryococcus braunii
X. Wang and P. E. Kolattukudy
Neurobiotechnology Center and Medical Biochemistry Department, The Ohio State University, 206 Rightmire Hall, 1060 Carmack Road, Columbus, Ohio 43210
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and a 66-kD
protein were co-purified from solubilized microsomal preparations of the
green alga Botryococcus braunii by Green A agarose, sucrose density
gradient, MonoQ, and gel filtration. The 66-kD protein remained intact
after 6 M urea treatment and sodium dodecyl sulfate-polyacrylamide gel
electrophoresis. It could be detected in the soluble fraction of the
cell-free extract but appeared to be more abundant in the microsomal
preparations. It cross-reacted with antibodies raised against Rubisco
holoenzyme, large and small subunits, indicating that the 66-kD protein
contains both the large and the small subunits of Rubisco. The N-terminal
amino acid sequence of this protein and that of a proteolytic fragment
showed high homology with the mature Rubisco small subunits, and the
sequence of another proteolytic fragment showed high homology with that of
the Rubisco large subunit. It is concluded that the 66-kD protein is
produced by cross-linking of large and small sub-units of Rubisco in the
cell.