Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301678
Title: Modified pigments and mechanisms of energy transfer in LH2 complexes from purple bacteria
Author: Fraser, Niall Johnston
ISNI:       0000 0001 2448 145X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1998
Availability of Full Text:
Access from EThOS:
Access from Institution:
Abstract:
The energy transfer processes in the LH2 complex from Rps. acidophila 10050 were investigated using a pigment-exchange strategy. In this approach, the Bchla-B800 molecules were selectively removed from their binding pockets and were replaced with modified pigments with altered spectral properties. Spectroscopic analysis of these modified complexes gave valuable insights into the mechanisms of energy transfer within the complex. The Bchla-B800 molecules can be released from their binding pockets by an acid treatment using buffer containing the novel Triton detergent TBGIO. B850-only complexes can then be purified by ion-exchange chromatography. Later, the empty B800 sites can be reconstituted with native Bchk. Maximal occupancy of the B800 sites can be obtained by incubating the B850-only complexes in buffer solution containing the detergent dodecyl-p-D- maltoside (LM) with a 3x fold excess of Bchla for 2 h at pH 8 and at room temperature. The Bchk-B800 reconstituted complex was fully characterised to determine how similar it is to native LH2. The average occupancy of the B800 sites in the Bchk-B800 reconstituted complex is ~ 80%. Resonance Raman spectroscopy showed that the reconstituted pigments are correctly bound within the complex and, as judged by CD spectroscopy, the structure of the LH complex is not affected by the pigment-exchange process. In addition, the reconstituted molecules participate in efficient B800?B850 energy transfer. Abstract The pigment-exchange protocol was then used with a series of modified pigments. The B800 binding sites can be reconstitued with geranylgeraniol Bchla, 132OH Bchla, Zn-Bphe, 31vinyl Bchla, 31OH Bchla, acetyl Chla and Chla. The B800 pockets can not be reconstituted with either pyro-Bchla, Cu- Bphe or Ni-Bphe. The 31vinyl Bchla-, 31OH Bchla-, acetyl Chla- and Chla- B800 reconstituted complexes are of particular interest as they have strongly blue-shifted "B800" Qy absorptions with maxima at 765, 751, 693 and 669 nm. CD spectroscopy again showed that the reconstituted pigments are correctly bound within the respective complexes. The occupancies of the B800 sites in the 31vinyl Bchla-, 31OH Bchla-, acetyl Chla- and Chla-B800 reconstituted complexes have yet to be accurately determined. In all of the reconstituted complexes, those pigment molecules which are correctly bound within the B800 binding pockets participate in efficient B800?B850 energy transfer. The kinetics of B800?B850 energy transfer in native and selected reconstituted complexes were studied by fs transient absorption spectroscopy. In both the native and Bchla-B800 reconstituted complexes, B800?B850 energy transfer takes approximately 0.9 ps. The time constants for B800?B850 energy transfer in the 3Vinyl Bchla-, 31OH Bchla-, acetyl Chla- and Chla-B800 reconstituted complexes are 1.4, 1.8, 4.4 and 8.5 ps respectively. This shows that the rate of B800-.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.301678  DOI: Not available
Keywords: Photosynthetic bacteria; Excitation transfer
Share: