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. Author manuscript; available in PMC: 2024 Jan 1.
Published in final edited form as: Nitric Oxide. 2022 Nov 30;130:58–68. doi: 10.1016/j.niox.2022.11.005

Figure 3. Time-dependent density functional theory (TDDFT) analysis of NO binding to cytochrome c oxidase (CcO).

Figure 3.

(A) A region around copper ion - NO - iron ion (Cu-(NO)-Fe) binding with porphyrin complex and histidine (His) was extracted from the whole CcO molecule (PDB: 5X1F). A copper ion is surrounded by three histidines, while NO binds to an iron ion coupled with a porphyrin structure and a histidine. (B-C) The time-dependent density functional theory (TDDFT) method was performed to calculate the excited states relevant to the NIR light absorption. (C) There are three multispectral absorbance peaks, which derive from the electronic transition from molecular orbital (MO) 203 (Highest Occupied Molecular Orbital: HOMO) to low-lying unoccupied orbitals (MOs 204-209). a: Absorption maxima, b: Corresponding transition energy calculated by TDDFT method, c: Oscillator strength. These results indicate that tissue treatment with NIR light leads to the NO release from CcO. Modified from Katagiri et al. 2020 [92] with permission from The International Society for Optical Engineering (SPIE).