ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

Hits per page

hits 1 - 2 | 2 hits

Sorting

Electronic Resource

Spectroscopic characterization of quinone-site mutants of the bacterial photosynthetic reaction center (1997)

Laible, Philip D. ; Zhang, Yuenian ; Morris, Andrea L. ; [et al.]

Springer

Photosynthesis research 52 (1997), S. 93-103

add to mindlist on the mindlist

Details

ISSN: 1573-5079

Keywords: electron paramagnetic resonance ; electron spin polarization ; quinone binding ; revertant isolation ; electrostatics

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Site-specific mutations in the quinone binding sites of the photosynthetic reaction center (RC) protein complexes of Rhodobacter (R.) capsulatus caused pronounced effects on sequential electron transfer. Conserved residues that break the twofold symmetry in this region of the RC – M246Ala and M247Ala in the QA binding pocket, and L212Glu and L213Asp in the QB binding pocket – were targeted. We constructed a QB-site mutant, L212Glu-L213Asp → Ala-Ala, and a QA-site mutant, M246Ala–M247Ala → Glu-Asp, to partially balance the differences in charge distribution normally found between the two quinone binding sites. In addition, two photocompetent revertants were isolated from the photosynthetically-incompetent M246Glu-M247Asp mutant: M246Ala–M247Asp and M246Gly–M247Asp. Sequential electron transfer was investigated by continuous light excitation and time-resolved electron paramagnetic resonance (EPR), and time-resolved optical techniques. Several lines of EPR evidence suggested that the forward electron transfer rate to QA, kQ, was slowed in those strains containing altered QA sites. The slower rates of secondary electron transfer were confirmed by time-resolved optical results with the M246Glu-M247Asp mutations in the QA site resulting in a dramatically lowered secondary electron transfer efficiency [kQ 〈 (2 ns)-1] in comparison with either the native R. capsulatus RC or the QB site mutant [kQ ≈ (200 ps)-1]. Secondary electron transfer in the two revertants was intermediate between that of the native RC and the QA mutant. The P+ QA- → PQA charge recombination rates were also changed in the strains that carried altered QA sites. We show that local mutations in the QA site, presumably through local electrostatic changes, significantly alter binding and electron transfer properties of QA.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1005806700335

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

Electronic Resource

Photorefractive liquid crystalsWe gratefully acknowledge support from the Office of Computational and Technological Programs, Division of Advanced Energy Projects, U. S. Department of Energy, under contract W-31-109-ENG-38. (1996)

Wiederrecht, Gary P. ; Yoon, Beth A. ; Wasielewski, Michael R.

Weinheim : Wiley-Blackwell

Advanced Materials 8 (1996), S. 535-539

add to mindlist on the mindlist

Details

ISSN: 0935-9648

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Photorefractive liquid crystals represent the newest class of photorefractive materials. The low electric fields required for reorienting liquid crystals, combined with their high birefringence, results in the observation of photorefractivity with very low optical intensities and low applied fields. Photoinducing efficient charge transport over macroscopic distances is the primary hurdle for producing the space-charge field required for photorefractivity.

Additional Material: 3 Ill.