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Biophysical Journal 85:3367-3374 (2003)
© 2003 The Biophysical Society

Role of the Aromatic Ring of Tyr43 in Tetraheme Cytochrome c3 from Desulfovibrio vulgaris Miyazaki F

Kiyoshi Ozawa {dagger}, Yuki Takayama *, Fumiko Yasukawa {dagger}, Tomoaki Ohmura {ddagger}, Michael A. Cusanovich §, Yusuke Tomimoto ¶, Hideaki Ogata ¶, Yoshiki Higuchi ¶ || and Hideo Akutsu * **

* Institute for Protein Research, Osaka University, Suita, Japan; {dagger} Faculty of Engineering, Yokohama National University, Yokohama, Japan; {ddagger} Yokohama Research & Development Center, Mitsubishi Heavy Industries, Yokohama, Japan; § Department of Biochemistry, University of Arizona, Tucson, Arizona; Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan; || RIKEN Harima Institute/SPring-8, Hyogo, Japan; and ** Institute for Molecular Science, Okazaki National Institutes, Okazaki, Japan

Correspondence: Address reprint requests to Hideo Akutsu, Osaka University, 3-2 Yamadaoka, Suita 565-0871, Japan. Tel.: 81-6-6879-8597; Fax: 81-6-6879-8599; E-mail: akutsu{at}protein.osaka-u.ac.jp.

Tyrosine 43 is positioned parallel to the fifth heme axial ligand, His34, of heme 1 in the tetraheme cytochrome c3. The replacement of tyrosine with leucine increased the redox potential of heme 1 by 44 and 35 mV at the first and last reduction steps, respectively; its effects on the other hemes are small. In contrast, the Y43F mutation hardly changed the potentials. It shows that the aromatic ring at this position contributes to lowering the redox potential of heme 1 locally, although this cannot be the major contribution to the extremely low redox potentials of cytochrome c3. Furthermore, temperature-dependent line-width broadening in partially reduced samples established that the aromatic ring at position 43 participates in the control of the kinetics of intramolecular electron transfer. The rate of reduction of Y43L cytochrome c3 by 5-deazariboflavin semiquinone under partially reduced conditions was significantly different from that of the wild type in the last stage of the reduction, supporting the involvement of Tyr43 in regulation of reduction kinetics. The mutation of Y43L, however, did not induce a significant change in the crystal structure.




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S.-m. Kim, T. Yamamoto, Y. Todokoro, Y. Takayama, T. Fujiwara, J.-S. Park, and H. Akutsu
Phospholipid-Dependent Regulation of Cytochrome c3-Mediated Electron Transport across Membranes
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