The 110-kDa reaction center protein of photosystem I, P700-chlorophyll a-protein 1, is an iron-sulfur protein.
1986; Elsevier BV; Volume: 261; Issue: 30 Linguagem: Inglês
10.1016/s0021-9258(18)67017-6
ISSN1083-351X
AutoresP B Høj, Birger Lindberg Møller,
Tópico(s)Metalloenzymes and iron-sulfur proteins
ResumoGermination and growth of barley (Hordeum uulgare L.) in the presence of ''Fez* or "SO:allows heavy incorporation of both isotopes into the thylakoid membranes and into isolated photosystem I particles.Analysis of '*Fe-Iabeled 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 SsS-labeled preparations, P700chlorophyll a-protein 1 binds zero valence 35S, which is converted into acid-labile [36S]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 law molecular weight polypeptides could be shown to be specifically associated with iron or acid-labile suffide.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 S8Fe-labeled thylakoids reveal other labeled polypeptides not associated with photosystem I, namely cytochrome f and possibly cytochromes be and ba,,.~ ~ ~ ~In higher plants, photochemical transfer of electrons from reduced plastocyanin to ferredoxin is catalyzed by PS I.' PS I is a membrane-bound protein complex containing several photoreducible electron acceptors (&, AI, X, A, B) (1).Centers A, and A, may be specialized chlorophyl~ molecules (2-5).Centers X, A, and B have been detected and identified as Fe-S centers using low temperature ESR spectroscopy (6,7).A comparative study with clostridial ferredoxin indicated that both centers A and B are 4 Fe-4 S centers (81, and their magnetic interaction suggests a close spatial arrangement possibly on the same polypeptide (9,lO).However, it has also
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