Mechanisms of photosystem I activity stimulation in trypsin-treated pea chloroplast membranes

Trypsin-induced effects on the PSI-photochemical activity of pea chloroplast membranes have been measured under saturating light conditions. It was found that incubation of isolated chloroplasts with trypsin in concentration range of 20–60 /smg trypsin per mg Chl leads to a linear increase of the rate of PSI-mediated electron transport, measured by O₂-uptake with methyl viologen as an electron acceptor and DCPIP·H₂ as electron donor. Low temperature (77 K) chlorophyll fluorescence measurements have indicated that a remarkable redistribution of excitation light energy in favor of PSI occurs under these conditions. The results are interpreted in terms of trypsin-induced lateral reorganization of the chlorophyll-protein complexes within the thylakoid membranes and specific alteration at the level of LHC a/b-PSII supramolecular organization.