Journal Article Distribution of valence electrons of the flavin cofactor in NADH-cytochrome b5 reductase

玉田, 太郎  ,  高場, 圭章(京都大学大学院理学研究科)  ,  竹田, 一旗(京都大学大学院理学研究科)  ,  小杉, 正幸(京都大学大学院理学研究科)  ,  三木, 邦夫(京都大学大学院理学研究科)

Flavin compounds such as flavin adenine dinucleotide (FAD), flavin mononucleotide and riboflavin make up the active centers in flavoproteins that facilitate various oxidoreductive processes. The fine structural features of the hydrogens and valence electrons of the flavin molecules in the protein environment are critical to the functions of the flavoproteins. Here we report the charge density analysis of a flavoenzyme, NADH-cytochrome b5 reductase (b5R), at an ultra-high resolution of 0.78 Å. Valence electrons on the FAD cofactor as well as the peptide portion, which are clearly visualized even after the conventional refinement, are analyzed by the multipolar atomic model refinement. The topological analysis for the determined electron density reveals the valence electronic structure of the isoalloxazine ring of FAD and hydrogen-bonding interactions with the protein environment.

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