Isotope substitution of H2O by 2H2O causes an increase in the rate of dark recombination between photooxidized
bacteriochlorophyll (P+) and reduced primary
quinone acceptor in Rhodobacter sphaeroides reaction centers (RC) at room temperature. The isotopic effect declines upon decreasing the temperature.
Dehydration of RC complexes of Ectothiorhodospira shaposhnikovii chromatophores containing multiheme
cytochrome c causes a decrease in the efficiency of transfer of a photomobilized electron between the primary and secondary
quinone acceptors and from
cytochrome to P+. In the case of H2O medium these effects are observed at a lower hydration than in 2H2O-containing medium. In the E. shaposhnikovii chromatophores subjected to
dehydration in H2O, the rate of electron transfer from the nearest high-potential
cytochrome heme to P+ is virtually independent of hydration within the P/P0 range from 0.1 to 0.5. In samples hydrated in 2H2O this rate is approximately 1.5 times lower than in H2O. However, the isotopic effect of this reaction disappears upon
dehydration. The intramolecular electron transfer between two high-potential hemes of
cytochrome c in samples with 2H2O is inhibited within this range of P/P0, whereas in RC samples with H2O there is a trend toward gradual inhibition of the interheme electron transfer with
dehydration. The experimental results are discussed in terms of the effects of
isotope substitution and
dehydration on relaxation processes and charge state of RC on implementation of the reactive states of RC providing electron transfer control.