Room-temperature vibrational difference spectrum for S2QB-/S1QB of photosystem II determined by time-resolved Fourier transform infrared spectroscopy

Time-resolved FTIR spectroscopy has been used to kinetically characterize the vibrational properties of intact photosystem II-enriched membrane samples undergoing the S(1)Q(B)-to-S(2)Q(B)(-) transition at room temperature. To optimize the experimental conditions for the FTIR measurements, oxygen polarographic and variable chlorophyll a fluorescence measurements were used to define the decay of S-2 and Q(A)(-), respectively. The flash-induced S(2)Q(B)(-)/S(1)Q(B) difference spectra were measured at a temporal resolution of 4.44 s and a spectral resolution of 4 cm(-1). An intense positive band is observed at 1480 cm(-1) in the difference spectrum and shows a slow decay with a half time of similar to 13 s. Based on its decay kinetics and analogy to the infrared absorption of Q(A)(-) of photosystem II and Q(B)(-) in bacterial reaction centers, we conclude that the 1480 cm(-1) band arises from Q(B)(-) of PSII and tentatively assign it to the upsilon(CO) mode of the semiquinone anion Q(B)(-). The infrared spectral features attributed to the S-1-to-S-2 transition of the Mn cluster at room temperature show striking similarity to the S-2/S-1 difference spectrum measured at cryogenic temperatures (Noguchi, T., One, T.-A., and Inoue, Y. (1995) Biochim. Biophys. Acta 1228, 189-200).