TRYPSIN-INDUCED CHANGES IN ENERGY-DISTRIBUTION BETWEEN PHOTOSYSTEM-I AND PHOTOSYSTEM-II IN PEA THYLAKOID MEMBRANES

The influence of ''mild'' trypsin digestion of pea thylakoid membranes on fluorescence emission and excitation spectra was investigated. Wit h increasing trypsin concentration the intensity of fluorescence emiss ion 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 mu g tryp/mg Chi. This inc rease was more pronounced when the excited light wavelength was 472 nm . In order to clarify which chlorophyll forms are responsible for thes e changes in the distribution of light energy between both photosystem s, an analysis of fluorescence excitation spectra in ''blue'' and ''re d'' regions was carried out. In the ''blue'' region an increase of the ratio of intensities 470/436 was observed. In the ''red'' region an i ncrease of the intensity of the shoulder at 650 nm is observed. Concom itantly, a shift to shorter wavelengths of the excitation maximum at 6 80 nm was observed. The data presented support the view that the obser ved increase of photosystem I energy supply involves an increased cont ribution of Chi b molecules.