水溶液中のヘムタンパク質のスピン状態の観測に成功 ―ミオグロビン水溶液の軟X線吸収分光測定―

2026-09-07 分子科学研究所

図1 : 25 °Cの水溶液中のミオグロビンのヘムのN K吸収端XASスペクトル。(a) oxyMb, (b) deoxyMb, (c) metMbのポルフィリン環のC=N π*ピークと分子構造を示す。内殻励起計算との比較により、異なる状態のヘムのスピン状態を明らかにした。

＜関連情報＞

• https://www.ims.ac.jp/news/2026/09/0907.html
• https://pubs.rsc.org/cp/article/doi/10.1039/D6CP00764C/1294252/Spin-states-of-myoglobin-heme-iron-in-aqueous

ポルフィリン環の窒素K吸収端X線吸収分光測定による室温の水溶液中のミオグロビンのヘムのスピン状態の観測

Spin states of myoglobin heme iron in aqueous solutions at room temperature probed from porphyrins using nitrogen K-edge X-ray absorption spectroscopy

yasunobu sugimoto;Shota Tsuru;Masanari Nagasaka

Physical Chemistry Chemical Physics  Published:24 August 2026

DOI:https://doi.org/10.1039/D6CP00764C

The porphyrin C=N π* peaks of myoglobin heme iron in aqueous solutions at room temperature were observed using nitrogen K-edge X-ray absorption spectroscopy (XAS), which enabled separation from the protein polypeptide peaks. The spin states of the heme iron were investigated by interpreting the C=N π* peaks through inner-shell calculations. Oxymyoglobin, in which an Fe²⁺ ion is connected to an oxygen molecule, is in the S = 0 state. By contrast, deoxymyoglobin with an Fe²⁺ ion shows a spin equilibrium between the S = 2 and 1 states, while metmyoglobin with an Fe³⁺ ion coordinated to a water molecule shows a spin equilibrium between the S = 5/2 and 3/2 states. This study proposes that N K-edge XAS measurements of porphyrins are effective for determining the spin equilibrium of heme proteins, which is influenced by liquid temperature and protein structure.