Topographical studies of the polypeptide subunits of the thylakoid cytochrome b6-f complex.
The orientation of specific polypeptides of the cytochrome b6-f complex with respect to the chloroplast stromal phase has been studied using trinitrobenzenesulfonate (TNBS) and pronase E as impermeant modifying reagents. Of the four polypeptides of the complex (33,23,20 and 17 kDa), only cytochrome f was labeled by 14C-TNBS in unfractionated membranes. However, to a varying degree, all of the constituent polypeptides were sensitive to pronase digestion and, in the case of cytochrome f, it was possible, by immunoblotting techniques to identify several degradation products. These results are discussed in relation to the organization of the cytochrome complex in thylakoid membranes and argue for an exposure to the stromal phase of all of the polypeptides, while functional considerations indicate that at least cytochrome f and the Rieske iron-sulfur protein have a possible transmembrane organization.
D000818:Animals; D002736:Chloroplasts / Q000032:analysis*; D003573:Cytochrome b Group / Q000032:analysis*; D045346:Cytochrome b6f Complex; D003580:Cytochromes / Q000032:analysis*; D045348:Cytochromes f; D010455:Peptides / Q000032:analysis*; D011402:Pronase / Q000494:pharmacology; D011817:Rabbits; D014302:Trinitrobenzenesulfonic Acid
D003573:Cytochrome b Group; D003580:Cytochromes; D010455:Peptides; D014302:Trinitrobenzenesulfonic Acid; D045346:Cytochrome b6f Complex; D045348:Cytochromes f; D011402:Pronase