Photoelectric studies of the transmembrane charge transfer reactions in photosystem I pigment‐protein complexes

Abstract

The results of studies of charge transfer in cyanobacterial photosystem I (PS I) using the photoelectric method are reviewed. The electrogenicity in the PS I complex and its interaction with natural donors (plastocyanin, cytochrome c 6 ), natural acceptors (ferredoxin, £avodoxin), or arti¢cial acceptors and donors (methyl viologen and other redox dyes) were studied. The operating dielectric constant values in the vicinity of the charge transfer carriers in situ were calculated. The pro¢le of distribution of the dielectric constant along the PS I pigmentp rotein complex (from plastocyanin or cytochrome c 6 through the chlorophyll dimer P700 to the acceptor complex) was estimated, and possible mechanisms of correlation between the local dielectric constant and electron transfer rate constant were discussed. ß

Dielectric and photoelectric properties of photosynthetic reaction centers

“…Like in the case of the BRC (see Table 1), the ε value in the protein domain between the Chl (bacteriochlorophyll) dimer and Q A is the lowest, whereas it gradually increases at the donor side. A similar increase in the effective dielectric constant is observed at the donor side of PS I [11,12]. Note that the ε value in the domain between Y Z and P680 is only ~1.5 times higher than that at the P680-Q A region, while the ε values in the Pc-P700 and cyt c 559 -P960 protein regions of PS I and BRC, respectively, increase about threefold relative to the hydrophobic core domains (Tables 1 and 2), which is seemingly consistent with higher electron transfer rate (30 nsec [22]) compared to that at the donor sides of PS I and BRC (microsecond to millisecond lifetime range).…”

“…The lifetimes of the electron and proton transfer reactions on the acceptor side of BRC (submillisecond time range) are at least three orders of magnitude lower than those values at the domain of the iron sulfur clusters in PS I (range of tens to hundreds of nanoseconds). Perhaps, the three order of magnitude difference between the rate constants of charge transfer on the acceptor side of BRC and PS I, and threefold increase in the estimated value of ε reflects the hypothet ical correlation between the reaction rates and the dielec tric properties of the corresponding protein domains between redox cofactors suggested in our earlier works [11,12].…”

“…In the preceding works we obtained the following estimates of ε distribution along the electron transfer chain in the pigment-protein complexes of PS I: ε~ 5.4 (Α 0 →Α 1 and Α 1 →F X ), ε~ 8.7 (F X →F A ), and ε~ 4.6 (F A →F B ) [11,12]. These estimates of ε are qualitatively consistent with the pattern of distribution of water mole cules and ionizable amino acid residues (Asp, Glu, Lys, Arg, and His) in the loci of the electron transfer chain.…”

“…Photoelectric and dielectric properties of PS I were considered in our earlier reviews [11,12]. The goal of this work was to review photoelectric and dielectric properties of BRC and PS II and to discuss possible mechanisms of correlation between values of charge transfer reaction rate constant and dielectric permittivity of photosynthetic pigment-protein complexes noted in the preceding works Abstract-A brief review of studies of dielectric and photoelectric properties of photosynthetic reaction centers of purple bac teria as well as photosystem I and photosystem II of cyanobacteria and higher plants is given.…”

“…70 No. 2 2005 [11,12]. The results of X ray diffraction analysis of crys tals of the protein complex of photosynthetic RC were from the Brookhaven Protein Databank (http:// www.rcsb.org/pdb).…”