Mutational Analyses of the Photosynthetic Reaction Center-Bound Triheme Cytochrome Subunit and Cytochrome c2 in the Purple Bacterium Rhodovulum sulfidophilum

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• 作者：Shinji Masuda ; Yusuke Tsukatani ; Yasuaki Kimura ; Kenji V. P. Nagashima ; Keizo Shimada ; and Katsumi Matsuura
• 刊名：Biochemistry
• 出版年：2002
• 出版时间：September 17, 2002
• 年：2002
• 卷：41
• 期：37
• 页码：11211 - 11217
• 全文大小：111K
• 年卷期：v.41,no.37(September 17, 2002)
• ISSN：1520-4995

文摘

The purple photosynthetic bacterium Rhodovulum sulfidophilum has an unusual reaction center-(RC-) bound cytochrome subunit with only three hemes, although the subunits of other purple bacteriahave four hemes. To understand the electron-transfer pathway through this subunit, three mutants of R.sulfidophilum were constructed and characterized: one lacking the RC-bound cytochrome subunit, anotherone lacking cytochrome c₂, and another one lacking both of these. The mutant lacking the RC-boundcytochrome subunit was grown photosynthetically with about half the growth rate of the wild type, indicatingthat the presence of the cytochrome subunit, while not indispensable, is still advantageous for thephotosynthetic electron transfer to support its growth. The mutant lacking both the cytochrome subunitand cytochrome c₂ showed a slower rate of growth by photosynthesis (about a fourth of that of the wildtype), indicating that cytochrome c₂ is the dominant electron donor to the RC mutationally devoid of thecytochrome subunit. On the other hand, the mutant lacking only the cytochrome c₂ gene grewphotosynthetically as fast as the wild type, indicating that cytochrome c₂ is not the predominant donor tothe RC-bound triheme cytochrome subunit. We further show that newly isolated soluble cytochrome c-549with a redox midpoint potential of +238 mV reduced the photooxidized cytochrome subunit in vitro,suggesting that c-549 mediates the cytochrome c₂-independent electron transfer from the bc₁ complex tothe RC-bound cytochrome subunit. These results indicate that the soluble components donating electronsto the RC-bound triheme cytochrome subunit are somewhat different from those of other purple bacteria.