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TSUBAKI, Motonari (Professor)

鍔木 基成 (教授)

Specialized Field
Biomolecular Science
Research Interests

Biomembranes are essential for many biological functions participatedby living organisms. They are not just the barrier discriminating the inner system from the outer space. They provide places for exchanging information, various substances, and energy required for the living organisms. For these reasons,elucidation of structure and function of membrane proteins and enzymes are the most important for better understanding of living life systems. Membrane proteins and enzymes have many difficulties as a research target.

(1) Purification of the membrane proteins is very difficult due to their intrinsic hydrophobicity.
(2) For their solubiliazation and purification, usage of detergents are inevitable. However, the presence of detergents in the sample solution will interrupt the formation of the membrane protein crystals in good quality. Indeed, there are still only a few membrane proteinX-ray crystal structures in atomic resolution are available.
(3) Precise understanding of biological roles of these membrane proteins and enzymes are very difficult since their true functions may be obscured upon solubilization from biomembranes. These difficulties, however, make the membrane proteins and enzymes to be very attractive frontier for the understanding to living systems.

Our research group has been studying in the field of membrane proteins and enzymes, particularly hemoproteins; such as various cytochrome P450, cytochrome c oxidase, ubiquinol oxidase, cytochrome b561, dopamine b-hydroxylase. Our strategy for studying these membrane proteins and enzymes consists of three major methodologies.
(a) Purification of the membrane proteins and enzymes utilizing various molecular biological and biochemical techniques.
(b) Analyses of their structural and functional dynamics utilizing various biophysical and biochemical techniques including, stopped-flow, infrared, resonance Raman, pulse radiolysis, NMR, X-ray crystallography.
(c) To clarify the true functions of these membrane proteins and enzymes, we developed the proteoliposome system. In these reconstituted enzymatic system, their enzymatic reactions are analyzed to clarify the exact nature as membrane proteins.

Research Subjects
  • Physicochemical and biochemical analysis of steroid hormone hydroxylase systems in adrenal cortex
  • Structure and function of respiratory heme-copper terminal oxidases
  • Structure and function of respiratory heme-heme terminal oxidases
  • Electron transfer system in neuroendocrine vesicle membranesProtein design by laboratory evolution
Selected Publications

◆Existence of two heme B centers in cytochrome b561 from bovine adrenal chromaffin vesicles as revealed by a new purification procedure and EPR spectroscopy, M. Tsubaki, M. Nakayama, E. Okuyama, Y. Ichikawa, and H. Hori, J. Biol. Chem. 272, 23206-23210, (1997).

◆Structural basis for the electron transfer across the chromaffin vesicle membranes catalyzed by cytochrome b561: Analyses of cDNA nucleotide sequences and visible absorption spectra, Okuyama, E., R. Yamamoto, Y. Ichikawa, and M. Tsubaki, Biochim. Biophys.Acta 1383, 269-278, (1998).

◆Distinct roles of two heme centers for transmembrane electron transfer in cytochrome b561 from bovine adrenal chromaffin vesicles as revealed by pulse radiolysis, Kobayashi, K., .M. Tsubaki, and S. Tagawa, J. Biol. Chem. 273, 16038-16042, (1998).

◆Diethylpyrocarbonate-modification abolishes fast electron accepting ability of cytochrome b561 from ascorbate but does not influence on electron donation to monodehydroascorbate radical: Identification of the modification sites by mass spectrometric analyses, M. Tsubaki, K. Kobayashi, T. Ichise, F. Takeuchi, and S. Tagawa, Biochemistry 39, 3276-3284, (2000).

◆Ascorbate inhibits the carbethoxylation of two histidyl and one tyrosyl residues indispensable for the transmembrane electron transfer reaction of cytochrome b561, Takeuchi, F., K. Kobayashi, S. Tagawa, M. Tsubaki, Biochemistry, 40,4067-4076, (2001).

◆Adrenodoxin-cytochrome P450scc interaction as revealed by EPR spectroscopy: Comparison with putidaredoxin-cytochrome P450cam system, Takeuchi, K., Tsubaki, M., Futagawa, J., Masuya, F. and Hori, H., J. Biochem. 130, 789-797 (2001).

◆Planarian cytochrome b561: Conservation of asix transmembrane structure and localization along the central and peripheral nervous system, Asada, A., Kusakawa, T., Orii, H., Agata, K., Watanabe, K., and Tsubaki, M., J. Biochem. 131, 175-182 (2002).

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