Trypsin-induced changes in energy distribution between photosystem I and photosystem II in pea thylakoid membranes

Abstract

The influence of “mild” trypsin digestion of pea thylakoid membranes on fluorescence emission and excitation spectra was investigated. With increasing trypsin concentration the intensity of fluorescence emission maximum at 735 nm (attributed to PSI) was enhanced and the ratio F 735/ F 685 increased from 1.47 ± 0.12 for control thylakoids up to 3.15 + 0.23 for thylakoids, treated with 8 μg tryp/mg Chl. This increase was more pronounced when the excited light wavelength was 472 nm. In order to clarify which chlorophyll forms are responsible for these changes in the distribution of light energy between both photosystems, an analysis of fluorescence excitation spectra in “blue” and “red” regions was carried out. In the “blue” region an increase of the ratio of intensities 470/436 was observed. In the “red” region an increase of the intensity of the shoulder at 650 nm is observed. Concomitantly, a shift to shorter wavelengths of the excitation maximum at 680 nm was observed. The data presented support the view that the observed increase of photosystem I energy supply involves an increased contribution of Chl b molecules.