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Inhibition of Photosynthetic Electron Transport in Spinach Chloroplasts by 2,6-Disubstituted Pyridine-4-thiocarboxamides

K. Kráľová, F. Šeršeň, M. Miletín, and M. Doležal

Institute of Chemistry, Faculty of Natural Sciences, Comenius University, SK-842 15 Bratislava

 

E-mail: kralova@fns.uniba.sk

Received: 10 January 2002

Abstract: Inhibition of oxygen evolution rate in spinach chloroplasts by 2,6-disubstituted pyridine-4- thiocarboxamides (R1 = SCH3, SC2 H5, SC3 H7, SC4H9, SC5H11, SC6H13, SC7H15, SC8H17; R2 = SCH3, SC2H5, SC3H7, SC4H9, SC5H11, Cl, Br) was investigated. The determined IC50 values varied in the range from 9.3 μmol dm−3 (R1 = SC3H7; R2 = Cl) to 342.0 μmol dm−3 (R1 = R2 = SCH3). The dependence of the biological activity on the lipophilicity of the compounds showed a bilinear course for compounds with R2 = halogen and a quasi-parabolic course for compounds with R1 = R2 = alkylsulfanyl. At comparable log {P} values the compounds containing halogen atom in their molecules exhibited significantly higher biological activity than the 2,6-dialkylsulfanyl derivatives. Using EPR spectroscopy it was found that the studied compounds interacted with the intermediate D, i.e. tyrosine radical (TyrD) situated in the 161st position in D2 protein on the donor side of photosystem (PS) 2. Due to this interaction the photosynthetic electron transport between PS 2 and PS 1 was interrupted. The primary donor of PS 2 (P680) remained intact.

Full paper in Portable Document Format: 563a214.pdf

 

Chemical Papers 56 (3) 214–217 (2002)

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