Effect of Alcohols on Inhibition of Photophosphorylation and Electron Transport by N,N'-Dicyclohexylcarbodiimide in Pea Chloroplasts

E. K. Zolotareva,^1,2 A. F. Tereshchenko,¹ E. F. Dovbysh,¹ and E. B. Onoiko¹

¹Kholodnyi Institute of Botany, National Academy of Sciences of Ukraine, ul. Tereshchenkovskaya 2, Kiev, 252601 Ukraine; fax: (044) 224-10-64; E-mail: ezol@botan.kiev.ua

²To whom correspondence should be addressed.

Submitted October 16, 1996; revision submitted February 25, 1997.

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The effect of solvent concentration (methanol, ethanol, and dimethylsulfoxide) on the inhibition of photophosphorylation and uncoupled electron transport from H₂O to methylviologen by N,N'-dicyclohexylcarbodiimide (DCCD) was studied in pea chloroplasts. In the absence of DCCD the solvents in concentrations up to 1.5% did not influence the rate of cyclic and non-cyclic photophosphorylation and uncoupled electron transport from H₂O to methylviologen. DCCD inhibited these reaction and the presence of methanol or ethanol potentiated its effect. Increase of methanol concentration from 0.1 to 0.5% was accompanied by a decrease of IC₅₀ for DCCD-dependent inhibition of uncoupled electron transport from 0.12 to 0.014 mM. Similar changes in the ethanol concentrations resulted in a decrease of IC₅₀ from 0.15 to 0.028 mM. With dimethylsulfoxide as solvent (up to 0.5%) DCCD did not inhibit uncoupled electron transport. DCCD-Dependent inhibition of cyclic (in the presence of phenazine methosulfate) and non-cyclic (in the presence of methylviologen) photophosphorylation did not depend on the solvent concentration in the medium up to 0.5% dimethylsulfoxide and 0.2 mM DCCD. These data indicate that inhibition of photophosphorylation by DCCD in the presence of dimethylsulfoxide occurs mainly due to inhibition of chloroplast ATP-synthetase whereas in the presence of alcohols the inhibition involves methanol- or ethanol-dependent blockade of electron transport. This effect can be associated with DCCD-mediated esterification of functionally essential groups of protein components of the chloroplast electron transport chain.

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KEY WORDS: N,N'-dicyclohexylcarbodiimide, photophosphorylation, electron transport, chloroplasts.

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