ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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 (Tyr^•_D) 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)