Biophysical investigation of electron transfer between high-potential hemes in c subunit and special pair of reaction center protein of photosynthetic bacteria Rhodopseudomonas viridis
Neshich, Goran
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https://hdl.handle.net/2142/22830
Description
Title
Biophysical investigation of electron transfer between high-potential hemes in c subunit and special pair of reaction center protein of photosynthetic bacteria Rhodopseudomonas viridis
Author(s)
Neshich, Goran
Issue Date
1989
Doctoral Committee Chair(s)
Wraight, Colin A.
Department of Study
Biophysics and Computational Biology
Discipline
Biophysics and Computational Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biophysics, General
Language
eng
Abstract
Bacterium Rhodopseudomonas viridis has four c-type cytochromes integrated to a single protein subunit of the reaction center complex. Two of them are high redox midpoint potential hemes (cyt-c559; Em = 380 mV and cyt-c556; Em = 310 mV) and other two are low midpoint potential hemes (cyt-c552; Em = 0 mV and cyt-c554; Em = $-$60 mV). The temperature dependence of the rate of oxidation of high potential cytochrome following absorption of a short pulse of light from a ruby laser has been measured spectrophotometrically. At redox potential Eh about 200 to 250 mV both high potential cytochromes are capable of donating an electron to the oxidized primary donor. Under these conditions the absorbance change observed at 554 nm is characterized by two component exponential decays due to cytochrome oxidation. The fast phase is due to electron transfer from the heme nearest to the P$\sp+$, while slow phase is explained in terms of electron sharing between the two high-potential hemes. The half times were determined to be t$\sb{1/2}$(295 K) = 1.7 $\pm$ 0.3 $\mu$s and t$\sb{1/2}$(74 K) = 10 $\pm$ 2 ms for the slow phase and t$\sb{1/2}$(295 K) = 0.18 $\pm$ 0.02 $\mu$s and t$\sb{1/2}$(74 K) = 0.41 $\pm$ 0.05 ms for the fast phase. Calculated activation energies are 8.4 Kcal/Mol for the slow phase and 10.1 Kcal/Mol for the fast phase. The effect of low potential cyt-c552 placed between two high potential hemes is on increased (about exp(22) times) probability of electron tunneling.
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