A study was made of electric phenomena in isolated photosynthetically-active chloroplast membranes upon energization. Energization of chloroplast thylakoid membranes gives rise to a charge separation across the membrane and an associated transmembrane electric field. The kinetics of this field were monitored as potential changes by a micro-electrode inserted in a single chloroplast and they were compared with the absorbance change of an intrinsic pigment (P515) proposed to be a reflection of a transmembrane electric field. The observed discrepancy between the flash-induced PSIS response and the electric response was caused by conformational changes in the membranal core that brought about absorbance changes of P515 in addition to its reponsiveness to the transmembrane potential. Most of the conclusions drawn hitherto from P515 kinetics, both after flash excitation and during prolonged illumination, have to be regarded with caution because they commonly are based on assumptions that are invalid under normal physiological conditions. Under certain conditions, if appropriate corrections are made, the PSIS kinetics are indeed a reflection of the transmembrane potential. In that case the results appear to be in good agreement with results obtained with the electrophysiological approach.<p/>The component of the P515 absorbance change, that is ascribed to conformational changes in the membranal core, may provide a useful tool for studies of fast structural changes in relation to energy coupling, without affecting the membrane integrity.
|Qualification||Doctor of Philosophy|
|Award date||10 Dec 1980|
|Place of Publication||Wageningen|
|Publication status||Published - 1980|
- electrical properties