title: The 110-kDa reaction center protein of photosystem I, P700-chlorophyll a-protein 1, is an iron-sulfur protein.
abstract: Germination and growth of barley (Hordeum vulgare L.) in the presence of 59Fe2+ or 35SO4(2-) allows heavy incorporation of both isotopes into the thylakoid membranes and into isolated photosystem I particles. Analysis of 59Fe-labeled preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under mild conditions demonstrates that a minimum of four iron atoms/P700 is carried on P700-chlorophyll a-protein 1. When isolated from 35S-labeled preparations, P700-chlorophyll a-protein 1 binds zero valence 35S, which is converted into acid-labile [35S]sulfide by dithiothreitol reduction. Isolated photosystem I particles contain 14 acid-labile sulfide atoms and 10 iron atoms for each molecule of P700 and are composed of polypeptides of 110, 18, 15, 10, and 8 kDa of which the 10-kDa component is loosely bound. Under the electrophoretic conditions used, none of the low molecular weight polypeptides could be shown to be specifically associated with iron or acid-labile sulfide. Carboxymethylation of cysteine residues shows a high cysteine content in the 8-kDa polypeptide and an intermediate content in the 110- and 18-kDa polypeptides, whereas the 15-kDa polypeptide is devoid of sulfur amino acids. The experiments with the 59Fe-labeled thylakoids reveal other labeled polypeptides not associated with photosystem I, namely cytochrome f and possibly cytochromes b6 and b559.
mesh_terms: D002734:Chlorophyll / Q000032:analysis*; D000077194:Chlorophyll A; D004229:Dithiothreitol / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D001467:Hordeum; D007506:Iron-Sulfur Proteins / Q000032:analysis*; D045342:Light-Harvesting Protein Complexes; D008667:Metalloproteins / Q000032:analysis*; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000032:analysis*
chemical_list: D007506:Iron-Sulfur Proteins; D045342:Light-Harvesting Protein Complexes; D008667:Metalloproteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D004229:Dithiothreitol; D000077194:Chlorophyll A