PHOTOINDUCED VOLUME CHANGES ASSOCIATED WITH THE EARLY TRANSFORMATIONSOF BACTERIORHODOPSIN - A LASER-INDUCED OPTOACOUSTIC SPECTROSCOPY STUDY

Volume changes associated with the primary photochemistry of bacterior hodopsin (BR) were measured by temperature-dependent laser-induced opt oacoustic spectroscopy (LIOAS). Excitation was performed with 8-ns fla shes establishing a photoequilibrium between the BR and the K states ( BR half arrow right over half arrow left(hv) K). The concentration of K at the end of the laser pulse, which is an important parameter for t he calculation of the volume change per molecule from the LIOAS data, was determined by flash photolysis with optical detection under the sp ecific conditions (concentration, photon density) of the LIOAS experim ent. Temperature-dependent measurements yielded a linear dependency of the ratio of the optoacoustic signals for BR and for a calorimetric r eference (CoCl2) with the cubic thermal expansion coefficient beta of water. From the slope of this linear ratio a contraction of 11 cm(3)/m ol was determined.