title: Purification and properties of the intact P-700 and Fx-containing Photosystem I core protein.
abstract: The intact Photosystem I core protein, containing the psaA and psaB polypeptides, and electron transfer components P-700 through FX, was isolated from cyanobacterial and higher plant Photosystem I complexes with chaotropic agents followed by sucrose density ultracentrifugation. The concentrations of NaClO4, NaSCN, NaI, NaBr or urea required for the functional removal of the 8.9 kDa, FA/FB polypeptide was shown to be inversely related to the strength of the chaotrope. The Photosystem I core protein, which was purified to homogeniety, contains 4 mol of acid-labile sulfide and has the following properties: (i) the FX-containing core consists of the 82 and 83 kDa reaction center polypeptides but is totally devoid of the low-molecular-mass polypeptides; (ii) methyl viologen and other bipyridilium dyes have the ability to accept electrons directly from FX; (iii) the difference spectrum of FX from 400 to 900 nm is characteristic of an iron-sulfur cluster; (iv) the midpoint potential of FX, determined optically at room temperature, is 60 mV more positive than in the control; (v) there is indication by ESR spectroscopy of low-temperature heterogeneity within FX; and (vi) the heterogeneity is seen by optical spectroscopy as inefficiency in low-temperature electron flow to FX. The constraints imposed by the amount of non-heme iron and labile sulfide in the Photosystem I core protein, the cysteine content of the psaA and psaB polypeptides, and the stoichiometry of high-molecular-mass polypeptides, cause us to re-examine the possibility that FX is a [4Fe-4S] rather than a [2Fe-2S] cluster ligated by homologous cysteine residues on the psaA and psaB heterodimer.
authors.affiliation: Department of Chemistry, Portland State University, OR 97207.
authors.forename: K G
authors.initials: KG
authors.lastname: Parrett
authors.forename: T
authors.initials: T
authors.lastname: Mehari
authors.forename: P G
authors.initials: PG
authors.lastname: Warren
authors.forename: J H
authors.initials: JH
authors.lastname: Golbeck
mesh_terms: D001965:Bromides / Q000494:pharmacology; D002499:Centrifugation, Density Gradient; D002704:Chlorates / Q000494:pharmacology; D002734:Chlorophyll / Q000302:isolation & purification*; D003080:Cold Temperature; D003432:Cross-Linking Reagents; D000458:Cyanobacteria / Q000032:analysis; D004072:Digitonin / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005976:Glutaral; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D008970:Molecular Weight; D017830:Octoxynol; D010084:Oxidation-Reduction; D010777:Photochemistry; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000302:isolation & purification*; D011092:Polyethylene Glycols / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D017670:Sodium Compounds; D012974:Sodium Iodide / Q000494:pharmacology; D013053:Spectrophotometry; D013861:Thiocyanates / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
chemical_list: D001965:Bromides; D002704:Chlorates; D003432:Cross-Linking Reagents; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D017670:Sodium Compounds; D013861:Thiocyanates; D002734:Chlorophyll; D011092:Polyethylene Glycols; C024553:sodium thiocyanate; D014508:Urea; D017830:Octoxynol; D012964:Sodium; D012974:Sodium Iodide; D004072:Digitonin; C027938:sodium bromide; D005976:Glutaral; C032706:sodium chlorate