Thermodynamics of the primary and secondary photochemical reactions in Chromatium

Some observations on the primary acceptor of Rhodopseudomonas viridis

“…1 as an increase in extent of cytochrome oxidation. The potential at which this crossover occurred was essentially independent of pH between pH 6 and pH 9, and in this respect the change was similar to that observed in Chromatium chromatophores [8] . The change in the extent of cytochrome c oxidation 2 msec after the laser flash showed that at potentials between +130 mV and t50 mV a rapid decay appeared ( fig.…”

“…Several workers have used the low potential attenuation of the laser induced cytochrome c photo-oxidation in Chromatium chromatophores to estimate the redox potential of the primary acceptor [6,8,9]. We have applied this method to Rps.…”

Primary Events and the Trapping of Energy

“…Hmvever, the secondary donors and acceptors can, in many cases, transfer or accept more than one electron upon successive flashes or co11tinuing illumination (Parson, 1969b;Case and Parson, 1971). Once these secondary pools are emptied or filled, additional refractory periods or kinetic rate-limiting steps will be observed,…”

“…We can see pathways leading off in various directions; in many cases their topography is described in other chapters in this volune. (Case and Parson, 1971;Callis, Parson and Goutennan, 1972) show that the storage of free energy in the primary process in photosynthetic bacteria is primarily an entropy effect, and has little if any contribution from enthalpy or chemical bond energy sources. One way to interpret this finding is to view the primary process in terms of a photoinduced rearrangement of the electron distribution of the molecules in the reaction center complex, in a way that does not ~esult in an increase in the enthalpy of the system.…”

Membrane‐Bound c ‐Type Cytochromes in Heliobacillus mobilis

“…Recently, it was shown that two hemes/RC with redox potentials in this range were able to donate electrons to P798' . The observed difference in E,,, values between these two hemes photooxidised by the first and the second flashes (AE,,, = 20 mV) indicates the presence of either two similar hemes/RC with a redox midpoint potential corresponding to the average of the first-flash and second-tlash redox waves (Case and Parson, 1971), or the presence of two electrochemically distinct hemes . In these titrations of heme oxidations induced by a series of flashes, a component with E,,, = +90 mV was photooxidised by the third flash, probably corresponding to the heme with a midpoint potential of +80 m V 1 2 0 mV, which gives rise to the x> = 2.92 EPR signal.…”