Evidence for two different Rieske iron-sulfur proteins in the cytochrome bf complex of spinach chloroplast

Spinach thylakoids, grana vesicles, stroma lamellae vesicles and also isolated cytochrome bf complex, were analysed by two-dimensional polyacrylamide gel electrophoresis employing isoelectric focusing in the first dimension and sodium dodecyl-sulfate polyacrylamide gel electrophoresis in the second dimension. About 100 thylakoid membrane proteins were resolved. In all cases the Rieske FeS protein separated into two polypeptide spots having the isoelectric points of 5.1 and 5.4, respectively. The Rieske FeS protein was identified by immunoblot analysis and by microsequences of the first 23 N-terminal amino acids. The intensity of the Coomassie brilliant blue stain of the two spots was stronger for the Rieske FeS protein of the grana vesicles than for that of the stroma lamellae vesicles.