Biological photosensors studied by laser-induced optoacoustic spectroscopy

Abstract

In all biological photoreceptors (energy converters and signal sensors) light excitation generates sequences of several transients of lifetimes in the pico- to milliseconds range before eventually signal transduction takes place. The signal event is thus determined by the protein conformational changes concomitant with and subsequent to the primary event in the chromophore (e.g., isomerization or electron transfer). Due to the overlapping absorption spectra of the transients and the parent system in most photoreceptors, the study of the transient properties (such as yield and decay lifetimes) by optical methods is difficult if not impossible. Time-resolved evolution of the lighttriggered temperature and pression changes in solution, as studied by photothermal and photobaric methods (e.g., laser-induced optoacoustic spectroscopy, LIOAS), yields information on the lifetimes of these intermediates as well as on the enthalpic and structural changes (related to entropic changes) taking place upon formation of the intermediates, without recoursing to their optical properties [1, 2].