The effect of 18 compounds of the aryloxyaminopropanol type – potencial beta-adrenolytics (differing each from other by modifications in the hydrophilic and lipophilic part of the molecule) on the inhibition of oxygen evolution rate in spinach chloroplasts has been investigated. The compounds with n-octyloxymethyl and n-nonyloxymethyl group in position 3 of aromatic ring were found to exhibit the highest inhibitory activity (IC50 = 67, resp. 120 mmol dm -3 ). The compounds containing a heterocycle or the dimethylamino group in the hydrophilic part of the molecule and with propoxymethyl group on the aromatic ring were not active. Using EPR spectroscopy it was found that the studied compounds interact with Z + /D + intermediates, i.e. tyrosine radicals TyrZ and TyrD situated in D1 and D2 proteins on the donor side of photosystem 2. Higher concentrations of the studied inhibitors cause release of Mn 2+ ions from the oxygen evolving complex which is situated in photosystem 2. The interaction of the tested compounds with chlorophyll occurring in the photo- synthetic centres has been confirmed by fluorescence measurements as well.

        Key words: aryloxyaminopropanols – beta-adrenolytics – photosynthesis – EPR spectroscopy – spinach