Structural Studies of Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase
From studies of three crystal forms of ribulose bisphosphate (RuBP) carboxylase from Nicotiana tabacum (called I, II, and III), we have determined the subunit organization of RuBP carboxylase in increasing detail. Combined x-ray diffraction and electron microscope data from these crystals show that there must be some multiple of eight polypeptide chains in the molecule and that the polypeptides are arranged around a fourfold axis of symmetry. At low resolution the eight copies of each polypeptide are equivalent. In more formal terms, the RuBP carboxylase molecule is characterized by point group symmetry D4 (422, see Figure 1 below). The molecule has a square cross section, about 11 nm on an edge, and a cylindrical channel about 2 nm in diameter which runs along the fourfold axis perpendicular to the square cross section. Four large sub-units are arranged in a ring perpendicular to the fourfold axis, and two such rings are eclipsed, forming a two-level structure that extends about 10 nm along the fourfold axis.
KeywordsMolecular Image Large Subunit Small Subunit Uranyl Nitrate Point Group Symmetry
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- 9.Kwok, S. Y., Ph.D. Thesis, University of California, Los Angeles, 1972.Google Scholar