論文

査読有り 国際誌
2009年11月10日

Importance of the conserved lysine 83 residue of Zea mays cytochrome b(561) for ascorbate-specific transmembrane electron transfer as revealed by site-directed mutagenesis studies.

Biochemistry
  • Nobuyuki Nakanishi
  • ,
  • Motiur Md Rahman
  • ,
  • Yoichi Sakamoto
  • ,
  • Tadakazu Takigami
  • ,
  • Kazuo Kobayashi
  • ,
  • Hiroshi Hori
  • ,
  • Toshiharu Hase
  • ,
  • Sam-Yong Park
  • ,
  • Motonari Tsubaki

48
44
開始ページ
10665
終了ページ
78
記述言語
英語
掲載種別
研究論文(学術雑誌)
DOI
10.1021/bi9010682

Cytochromes b(561), a novel class of transmembrane electron transport proteins residing in a large variety of eukaryotic cells, have a number of common structural features including six hydrophobic transmembrane alpha-helices and two heme ligation sites. We found that recombinant Zea mays cytochrome b(561) obtained by a heterologous expression system using yeast Pichia pastoris cells could utilize the ascorbate/mondehydroascorbate radical as a physiological electron donor/acceptor. We found further that a concerted proton/electron transfer mechanism might be operative in Z. mays cytochrome b(561) as well upon the electron acceptance from ascorbate to the cytosolic heme center. The well-conserved Lys(83) residue in a cytosolic loop was found to have a very important role(s) for the binding of ascorbate and the succeeding electron transfer via electrostatic interactions based on the analyses of three site-specific mutants, K83A, K83E, and K83D. Further, unusual behavior of the K83A mutant in pulse radiolysis experiments indicated that Lys(83) might also be responsible for the intramolecular electron transfer to the intravesicular heme. On the other hand, pulse radiolysis experiments on two site-specific mutants, S118A and W122A, for the well-conserved residues in the putative monodehydroascorbate radical binding site showed that their electron transfer activities to the monodehydroascorbate radical were very similar to those of the wild-type protein, indicating that Ser(118) and Trp(122) do not have major roles for the redox events on the intravesicular side.

リンク情報
DOI
https://doi.org/10.1021/bi9010682
PubMed
https://www.ncbi.nlm.nih.gov/pubmed/19803484