Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA.
Photosynth Res. 2024 Mar;159(2-3):229-239. doi: 10.1007/s11120-023-01035-9. Epub 2023 Jul 7.
Microsecond time-resolved step-scan FTIR difference spectroscopy was used to study photosystem I (PSI) from Thermosynechococcus vestitus BP-1 (T. vestitus, formerly known as T. elongatus) at 77 K. In addition, photoaccumulated (P700-P700) FTIR difference spectra were obtained at both 77 and 293 K. The FTIR difference spectra are presented here for the first time. To extend upon these FTIR studies nanosecond time-resolved infrared difference spectroscopy was also used to study PSI from T. vestitus at 296 K. Nanosecond infrared spectroscopy has never been used to study PSI samples at physiological temperatures, and here it is shown that such an approach has great value as it allows a direct probe of electron transfer down both branches in PSI. In PSI at 296 K, the infrared flash-induced absorption changes indicate electron transfer down the B- and A-branches is characterized by time constants of 33 and 364 ns, respectively, in good agreement with visible spectroscopy studies. These time constants are associated with forward electron transfer from A to F on the B- and A-branches, respectively. At several infrared wavelengths flash-induced absorption changes at 296 K recover in tens to hundreds of milliseconds. The dominant decay phase is characterized by a lifetime of 128 ms. These millisecond changes are assigned to radical pair recombination reactions, with the changes being associated primarily with P700 rereduction. This conclusion follows from the observation that the millisecond infrared spectrum is very similar to the photoaccumulated (P700-P700) FTIR difference spectrum.
微秒时间分辨分步扫描傅里叶变换红外差谱法用于研究来自 Thermosynechococcus vestitus BP-1（T. vestitus，以前称为 T. elongatus）的光系统 I（PSI）在 77 K 下的情况。此外，还在 77 和 293 K 下获得了光积累（P700-P700）FTIR 差谱。这里首次呈现了 FTIR 差谱。为了扩展这些 FTIR 研究，还使用纳秒时间分辨红外差谱法研究了 296 K 下的 T. vestitus PSI。纳秒红外光谱法从未用于研究生理温度下的 PSI 样品，而这里表明，这种方法具有很大的价值，因为它可以直接探测 PSI 中两个分支的电子转移。在 296 K 下的 PSI 中，红外闪光诱导的吸收变化表明，电子从 B 和 A 分支向下转移的时间常数分别为 33 和 364 ns，与可见光谱研究非常吻合。这些时间常数分别与 B 和 A 分支上从 A 到 F 的前向电子转移相关。在几个红外波长下，296 K 下的闪光诱导吸收变化在数十到数百毫秒内恢复。主要的衰减相具有 128 ms 的寿命。这些毫秒变化被分配给自由基对重组反应，变化主要与 P700 再还原相关。这一结论是基于观察到毫秒红外光谱与光积累（P700-P700）FTIR 差谱非常相似得出的。
