Light Induced Changes in the Conformation of Spinach Thylakoid Membranes as Monitored by 90° and 180° Scattering Changes: A Comparative Investigation

Abstract

Abstract A series of investigations on light induced thylakoid membrane conformational changes has been carried out using scattering changes measured either at 90° or 180° (transmittance changes) as criteria for changes in membrane structure upon illumination. These two phenomena were found to react similarly to a range of photosynthetic inhibitors, to changes in the ionic (Mg2+, H+) concentration, and to have similar difference spectra. However, it was found possible to distinguish these two phenomena by the differences in the kinetics of the light induced rise times. This could be shown most clearly using an Aminco DW2 spectrophotometer with the measuring beam deflected through 90° by front face mirrors. The dark decay time of the two scattering changes was similar. These results are discussed in relation to the hypothesis that the light induced narrow angle 90° scattering response represents microconformational membrane changes in response to proton uptake, and the 180° scattering changes represent a mixed response including changes in the stacking of thylakoids.