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High Yield of B-Branch Electron Transfer in a Quadruple Reaction Center Mutant of the Photosynthetic Bacterium Rhodobacter sphaeroides
A new reaction center (RC) quadruple mutant, called LDHW, of Rhodobacter sphaeroides is described. This mutant was constructed to obtain a high yield of B-branch electron transfer and to study P+QB - formation via the B-branch. The A-branch of the mutant RC contains two monomer bacteriochlorophylls,...
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Published in: | Biochemistry (Easton) 2002-03, Vol.41 (9), p.3081-3088 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | A new reaction center (RC) quadruple mutant, called LDHW, of Rhodobacter sphaeroides is described. This mutant was constructed to obtain a high yield of B-branch electron transfer and to study P+QB - formation via the B-branch. The A-branch of the mutant RC contains two monomer bacteriochlorophylls, BA and β, as a result of the H mutation L(M214)H. The latter bacteriochlorophyll replaces bacteriopheophytin HA of wild-type RCs. As a result of the W mutation A(M260)W, the A-branch does not contain the ubiquinone QA; this facilitates the study of P+QB - formation. Furthermore, the D mutation G(M203)D introduces an aspartic acid residue near BA. Together these mutations impede electron transfer through the A-branch. The B-branch contains two bacteriopheophytins, ΦB and HB, and a ubiquinone, QB. ΦB replaces the monomer bacteriochlorophyll BB as a result of the L mutation H(M182)L. In the LDHW mutant we find 35−45% B-branch electron transfer, the highest yield reported so far. Transient absorption spectroscopy at 10 K, where the absorption bands due to the QX transitions of ΦB and HB are well resolved, shows simultaneous bleachings of both absorption bands. Although photoreduction of the bacteriopheophytins occurs with a high yield, no significant (∼1%) P+QB - formation was found. |
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ISSN: | 0006-2960 1520-4995 |
DOI: | 10.1021/bi011450m |