PHOTOCHEMICAL ENERGY-STORAGE AND VOLUME CHANGES IN THE MICROSECOND TIME RANGE IN BACTERIAL PHOTOSYNTHESIS - A LASER-INDUCED OPTOACOUSTIC STUDY

Native and modified reaction centers from Rhodobacter sphaeroides were investigated using laser-induced optoacoustic spectroscopy between 4 and 25 degrees C. The heat released within ca. 1 mu s of the laser pul se and the concomitant volume changes occurring upon molecular movemen ts are derived from these data. For the R-26 RC, an enthalpy change of 80 kJ mol(-1) (an energy storage of 40% at 590 nm) and an average con traction of 7+/-1 ml mol(-1) (corresponding to 12+/-2 Angstrom(3) per molecule) are attributed to the formation of the ion pair P(870)(+)IQ( A)(-). For the (M)Y210W mutant, different values for contraction and e nergy storage were obtained. Moreover, the contraction did not occur i n quinone-depleted reaction centers. A comparison of the signals from light-saturated centers with signals produced under low-light conditio ns leads to the conclusion that the quantum yield for the process of i on pair formation is 1.