Effects of Substituted Salicylanilides on the Photosynthetic Apparatus of Spinach Chloroplasts

Lenka Kubicová¹ (kubicova@faf.cuni.cz), Katarína Kráľová², František Šeršeň², Jiří Gregor¹, Karel Waisser¹

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

Summary

The inhibitory activity of 10 substituted salicylanilides (R = H, 4'-CH₃, 4'-Br, 4'-OCH₃, 4'-Cl, 3',4'-Cl₂, 3'-Cl, 3'-NO₂, 4'-NO₂, 4'-N(CH₃)₂) on oxygen evolution rate in spinach chloroplasts has been investigated. The IC₅₀ values in the investigated set varied in the range from 4 µmol dm^-3 (for R = 3'-Cl) to 339.8 µmol dm^-3 (for R = 4'-N(CH₃)₂). The inhibitory activity of the studied compounds correlates with the hydrophobic parameter pi^- and the Hammett constant sigma of the substituents. Using EPR spectroscopy, the intermediate D⁺, i. e. tyrosine radical situated in position 161 in D₂ protein on the donor side of photosystem 2 was identified as the site of action of these compounds in the photosynthetic apparatus of spinach chloroplasts.