Event Title

F700-FA/FB Recombination Dynamics of Quinones in the A1 Site of PS I Complexes of the Mutants of Synechocystis sp. PCC 6803 at Low Temperature

Faculty Advisor

Wade Johns

Start Date

25-4-2017 5:00 PM

End Date

25-4-2017 6:00 PM

Description

In photosystem I of higher plants and cyanobacteria, phylloquinone (PhQ) acts as the secondary electron acceptor occupying the A1 site between A0 and the Fe-S clusters of the electron transport chain. Phylloquinone-less mutants, menA and menB, of the cyanobacterium Synechocystis sp. PCC 6803 have plastoquinone (PQ) occupying the A1 site and is capable of functioning as the electron acceptor in place of PhQ. Here we report experiments in which the growth medium of the mutant cells was supplemented with highly reducing 9,10-anthraquinones (AQ). As a result, the menA and menB mutants appeared to utilize the anthraquinone in the A1 site. The potentials of the supplemented AQ’s are significantly more reducing than either PhQ and PQ by as much as 400mV. Because of this, the quinones may approach or exceed the potential of the primary acceptor, A0, and lead to unusual electron transition behaviors. The function of quinone molecules in the A1 site of the mutants was monitored by a home built pump probe laser system. The probe beam monitors the recombination of the electron from the terminal FeS clusters of PSI (e.g. P700+/FA/B-) The P700 back reaction kinetic lifetime changes as a function of quinone. The plastoquinone mutants shows a 3ms lifetime and samples containing AQs (e.g. 1-NH2-AQ) having longer lifetimes (100+ms). In decreasing the temperature, lifetimes change as a function of electron transfer pathways options. Glycerol is used as a cryogen but also seems to have a direct effect on the lifetimes. Room temperature and low temperature experiments with menA 1-NH2AQ and menB26 conc. Trimer in various glycerol concentration show an altered lifetime. We suspect that these factors may play a role in extending the kinetic back reaction of the reducing AQ in the A1 site, resulting in a loss of the longer phase. We are currently characterizing and exploring these observations to develop a hypothesis on the effect.

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Apr 25th, 5:00 PM Apr 25th, 6:00 PM

F700-FA/FB Recombination Dynamics of Quinones in the A1 Site of PS I Complexes of the Mutants of Synechocystis sp. PCC 6803 at Low Temperature

In photosystem I of higher plants and cyanobacteria, phylloquinone (PhQ) acts as the secondary electron acceptor occupying the A1 site between A0 and the Fe-S clusters of the electron transport chain. Phylloquinone-less mutants, menA and menB, of the cyanobacterium Synechocystis sp. PCC 6803 have plastoquinone (PQ) occupying the A1 site and is capable of functioning as the electron acceptor in place of PhQ. Here we report experiments in which the growth medium of the mutant cells was supplemented with highly reducing 9,10-anthraquinones (AQ). As a result, the menA and menB mutants appeared to utilize the anthraquinone in the A1 site. The potentials of the supplemented AQ’s are significantly more reducing than either PhQ and PQ by as much as 400mV. Because of this, the quinones may approach or exceed the potential of the primary acceptor, A0, and lead to unusual electron transition behaviors. The function of quinone molecules in the A1 site of the mutants was monitored by a home built pump probe laser system. The probe beam monitors the recombination of the electron from the terminal FeS clusters of PSI (e.g. P700+/FA/B-) The P700 back reaction kinetic lifetime changes as a function of quinone. The plastoquinone mutants shows a 3ms lifetime and samples containing AQs (e.g. 1-NH2-AQ) having longer lifetimes (100+ms). In decreasing the temperature, lifetimes change as a function of electron transfer pathways options. Glycerol is used as a cryogen but also seems to have a direct effect on the lifetimes. Room temperature and low temperature experiments with menA 1-NH2AQ and menB26 conc. Trimer in various glycerol concentration show an altered lifetime. We suspect that these factors may play a role in extending the kinetic back reaction of the reducing AQ in the A1 site, resulting in a loss of the longer phase. We are currently characterizing and exploring these observations to develop a hypothesis on the effect.