Biophysical investigation of electron transfer between high-potential hemes in c subunit and special pair of reaction center protein of photosynthetic bacteria Rhodopseudomonas viridis

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 μs 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 μs 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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Biophysics and Computational Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Neshich, Goran

Contributors dc:contributor

• Wraight, Colin A.

• Biophysics, General

Statement dc:rights

• Copyright 1989 Neshich, Goran

Language dc:language

eng

Identifier

AAI9010969
(UMI)AAI9010969

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/22830