The Site of Action of some Anilides of Pyrazine-2-Carboxylic Acids in the Photosynthetic Apparatus

Martin Doležal¹ (dolezalm@faf.cuni.cz), Katarína Kráľová², František Šeršeň², Miroslav Miletín¹

¹Department of Pharmaceutical Chemistry and Drug Control, Charles University in Prague, Faculty of Pharmacy in Hradec Králové, Czech Republic
²Institute of Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic

Summary

The site of action of some anilides of pyrazine-2-carboxylic acids in the photosynthetic apparatus of spinach chloroplasts was studied using fluorescence and EPR spectroscopies. It was found that the studied compounds cause quenching of the chlorophyll fluorescence at 685 nm belonging mainly to the pigment—protein complexes in photosystem (PS) 2. The extent of the fluorescence quenching correlated with the effectiveness of the compounds concerning inhibition of oxygen evolution rate (OER) in spinach chloroplasts. Using EPR spectroscopy it was confirmed that the studied anilides interact with the intermediate D⁺ (Tyr_D), i. e. with the tyrosine radical, which is situated on the donor side of PS 2 at the 161th position of D₁ protein. It was found that the studied compounds inhibit OER not only in the suspension of spinach chloroplasts but also in the suspensions of Chlorella vulgaris. Introducing of Cl substituents into anilide as well as pyrazine moiety of the studied anilides enhanced the effectiveness of OER-inhibiting activity.