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Functional studies of the low molecular mass subunits and terminal electron acceptors F(A) and F(B) in photosystem I
Abstract
Electron transfer rates to P700$\sp+$ have been determined in wildtype and three interposon mutants ($psaE\sp-, ndhF\sp-$ and $psaE\sp- ndhF\sp-)$ of Synechococcus sp. PCC 7002. Different inhibitors were used for interfacing the photosynthetic reactions. Results indicate that PsaE is an indispensable component in the cyclic electron pathway around photosystem I. The P700$\sp+$ reduction rate in two mutants of Synechocystis sp. PCC 6803, $psaL\sp-$ and $psaF\sp-$/$psaJ\sp-,$ have been determined. The lack of PsaL and PsaF/PsaJ do not affect linear or cyclic electron flow around Photosystem I. Analysis of flash-induced absorption transients at 700 nm demonstrate that the absence of PsaF in a purified mutant Photosystem I complex did not affect the rate of P700$\sp+$ rereduction by cytochrome $c\sb{553}.$ This indicates that PsaF is not essential for the docking of cytochrome $c\sb{553}.$ The iron sulfur clusters have been reinserted in two Escherichia coli overproduced mutants of PsaC where cysteines 14 and 51 were converted into aspartic acid. Under oxidizing conditions, the EPR spectrum showed that the ($\sp3$Fe-4S) clusters were rebuilt in the aspartate-modified site of C14D (F$\sb{B}\sp{\*}$) and C51D (F$\sb{\rm A}\sp{\*}$) respectively. The E$\sb{\rm m}$ values for F$\sb{\rm B}\sp{\*}$ in C14D and C51D are $-$98mV, and both represent one-electron titrations. Under reducing conditions, the EPR spectra at 15 K showed that the (4Fe-4S) clusters F$\sb{\rm A}$ and F$\sb{\rm B}$ were assembled in the unmodified sites of C14D and C51D respectively. The E$\sb{\rm m}$ value for F$\sb{\rm A}$ in C14D is $-$523 mV and the E$\sb{\rm m}$ value for F$\sb{\rm B}$ in C51D is $-$580 mV, and both represent one-electron titrations. The mutant PsaC proteins, C14D and C51D, were rebound to the P700-Fx core. One (4Fe-4S) cluster was found an unmodified site, and a mixed ligand, (4Fe-4S) cluster was assembled in the aspartate-modified site. The electrochemical and electron spin resonance properties of these (4Fe-4S) clusters were investigated.
Subject Area
Biochemistry|Biophysics
Recommended Citation
Yu, Lian, "Functional studies of the low molecular mass subunits and terminal electron acceptors F(A) and F(B) in photosystem I" (1994). ETD collection for University of Nebraska-Lincoln. AAI9516596.
https://digitalcommons.unl.edu/dissertations/AAI9516596