Eckert H J, Wiese N, Bernarding J, Eichler H J, Renger G
Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Berlin, Germany.
FEBS Lett. 1988 Nov 21;240(1-2):153-8. doi: 10.1016/0014-5793(88)80358-2.
Absorption changes at 325 nm (delta A325) induced by 15 ps laser flashes (lambda = 650 nm) in PS II membrane fragments were measured with picosecond time-resolution. In samples with the reaction centers (RCs) kept in the open state (P I QA) the signals are characterized by a very fast rise (not resolvable by our equipment) followed by only small changes within our time window of 1.6 ns. In the closed state (PI QA-) of the reaction center the signal decays with an average half-life time of about 250 ps. It is shown that under our excitation conditions (E = 2 x 10(14) photons/cm2 per pulse) subtraction of the absorption changes in closed RCs (delta A closed 325) from those in open RCs (delta A open 325) leads to a difference signal which is dominated by the reduction kinetics of QA. From the rise kinetics of this signal and by comparison with data in the literature it is inferred that QA becomes reduced by direct electron transfer from Pheo- with a time constant of about 350 +/- 100 ps.
用皮秒时间分辨率测量了15皮秒激光脉冲（波长 = 650纳米）在PS II膜片段中诱导的325纳米处的吸收变化（ΔA325）。在反应中心（RCs）保持开放状态（P I QA）的样品中，信号的特征是快速上升（我们的设备无法分辨），随后在1.6纳秒的时间窗口内只有微小变化。在反应中心的关闭状态（PI QA-）下，信号以约250皮秒的平均半衰期衰减。结果表明，在我们的激发条件下（E = 2×10(14) 光子/平方厘米/脉冲），从开放RCs中的吸收变化（ΔA开放325）中减去关闭RCs中的吸收变化（ΔA关闭325），会得到一个以QA的还原动力学为主导的差异信号。从该信号的上升动力学以及与文献数据的比较可以推断，QA通过从去镁叶绿素（Pheo-）的直接电子转移而被还原，时间常数约为350±100皮秒。
