Molecular interactions of the redox‐active accessory chlorophyll on the electron‐donor side of photosystem II as studied by Fourier transform infrared spectroscopy

[摘要]

A Fourier transform infrared (FTIR) difference spectrum upon photooxidation of the accessory chlorophyll (Chl_z) of photosystem II (PS II) was obtained at 210 K with Mn-depleted PS II membranes in the presence of fericyanide and silicomolybdate. The observed Chl_z ⁺/Chl_z spectrum showed two differential bands at 1747/1736 and 1714/1684 cm⁻. The former was assigned to the free carbomethoxy C = 0 and the latter to the keto C = 0 that is hydrogen-bonded or in a highly polar environment. Also, the negative 1614 cm⁻ band assignable to the macrocycle mode indicated 5-coordination of the central Mg. The negative 1660 cm⁻¹ band, possibly due to the strongly hydrogen-bonded keto C = 0, may suggest oxidation of one more Chl_z, although an alternative assignment, the amide I mode of proteins perturbed by Chl_z oxidation, is also possible.

[学科分类] 生物化学/生物物理

[关键词] Photosynthesis;Photosystem II;Fourier transform infrared spectroscopy;Chlorophyll;Radical cation;Chl;chlorophyll a in vitro;Chlz;redox-active accessory chlorophyll of PS II;cyt b 559;cytochrome b 559;ESR;electron spin resonance;FTIR;Fourier transform infrared;MES;2-(N-morpholino)ethanesulfonic acid;P680;primary electron donor;PS II;photosystem II;QA;primary quinone acceptor;THF;tetrahydrofuran;Y d;tyrosine electron donor in the D2 subunit;Y z;tyrosine electron donor in the D1 subunit