title: Nearest-neighbor relationships of the constituent polypeptides in plastoquinol-plastocyanin oxidoreductase.
abstract: The nearest-neighbor relationship among the constituent polypeptides of the isolated plastoquinol-plastocyanin oxidoreductase from spinach chloroplasts has been investigated. (1) The isolated plastoquinol-plastocyanin oxidoreductase (the b6/f complex) is treated with various concentrations of the cross-linker glutaraldehyde. The treated b6/f complexes are then analyzed by SDS-polyacrylamide gel electrophoresis coupled with the immunodecoration of cross-link products by specific antibodies for each of the four prominent constituent polypeptides. Cytochrome b6 is found to be most resistant to forming any intermolecular cross-link products. At low concentrations of glutaraldehyde, the 'Rieske' iron-sulfur (Fe-S) protein and subunit IV of the b6/f complex, however, appear to form cross-link products with a relative molecular weight of 35 000. Dimers of cytochrome f and cytochrome f/Rieske protein cross-link products can also be detected. (2) When a Rieske Fe-S protein-depleted b6/f complex is used in place of the control b6/f complex, cytochrome b6 is less resistant to intermolecular cross-linking, while subunit IV does not form any 35 kDa cross-link product, unlike the case in control b6/f complex. Subunit IV is concluded to be closely associated with the Rieske Fe-S protein. This provides evidence that subunit IV is a bona fide component of the cytochrome b6/f complex, although no function can yet be assigned to it. The results are discussed in relationship to the spatial and functional relationships among the components of the b6/f complex.
authors.forename: E
authors.initials: E
authors.lastname: Lam
mesh_terms: D002736:Chloroplasts / Q000201:enzymology*; D003432:Cross-Linking Reagents; D003580:Cytochromes; D005976:Glutaral; D046911:Macromolecular Substances; D010088:Oxidoreductases; D010944:Plants; D013329:Structure-Activity Relationship
chemical_list: D003432:Cross-Linking Reagents; D003580:Cytochromes; D046911:Macromolecular Substances; D010088:Oxidoreductases; D005976:Glutaral