[Relation between structural-dynamic organization of reaction centers in Rhodobacter sphaeroides and picosecond steps...

The effect of deuteration, and the addition of glycerol and dimethylsulfoxide on the redox midpoint potential Em of bacteriochlorophyll of the special pair ¿PMPL¿, the rate of energy migration from bacteriopheophytin HM to ¿PMPL¿, and electron transfer from ¿PMPL¿ to HL and from HL to quinone QA in reaction centers of Rhodobacter sphaeroides was studied. It was shown that H2O-->D2O substitution did not change Em of the special pair, while the addition of 70% glycerol and 35% dimethylsulfoxide (v/v) increased the Em value by 30 and 45 mV, correspondingly. The rate constants of energy migration [formula: see text], charge separation [formula: see text], electron transfer to QA kQ remained unchanged upon the addition of glycerol. The isotopic substitution of water and addition of dimethylsulfoxide led to a 2-3-fold increase in km, ke and kQ values. The dependence of the potential of redox center on the dielectric constant epsilon was analyzed. It was shown that replacement of H2O by dimethylsulfoxide can increase Em by tens of millivolt. There was no correlation between changes in Em and the values of km, ke and kQ upon deuteration and addition of cryoprotectors. It was concluded that the processes of energy migration, charge separation, and electron transfer to the quinone acceptor are preceded by the solvation of states H*M, ¿P+MP-L¿* and [formula: see text].