Identification of Naturally Occurring Calmodulin Inhibitors in Plants and their Effects on Calcium- and Calmodulin-promoted Protein Phosphorylation

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While studying the calmodulin activity in post-climacteric apples, a heat stable, dialyzable component that inhibited calmodulin-promoted phosphodiesterase activity was detected. The compound(s) that inhibited calmodulin activity did not bind to Dowex-50, H^+ or Dowex-2, Cl^- and was exclusively present in the neutral fraction. The inhibitors irreversibly bound to polyvinylpolypyrrolidone indicating their phenolic nature. Fractionation of the neutral fraction on a C_<18>-μbondapak column and analysis for the inhibition of calmodulin-promoted phosphodiesterase activity showed significant inhibitory activity associated with fractions eluted 5 min, 15 min and 18 min after injection. Perdeuteriomethylation and combined gas chromatographic-mass spectrometric analysis of the inhibitors showed them to be flavonoids. (+)-Catechin was identified in the fraction eluted 5 min after injection that also showed maximum inhibition. Other flavonoids such as epicatechin, quercetin and naringenin also inhibited calmodulin-promoted phosphodiesterase activity. Among the phenolic compounds commonly encountered in plant tissue only caffeic acid inhibited calmodulin-promoted phosphodiesterase activity. Inhibition by catechin and caffeic acid could be reversed by increasing the calmodulin concentration in the assay mixture. Both catechin and caffeic acid inhibited Ca- and calmodulin-promoted phosphorylation of soluble proteins from corn coleoptiles. The physiological properties of flavonoids are discussed in light of this evidence.
日本植物生理学会の論文

Identification of Naturally Occurring Calmodulin Inhibitors in Plants and their Effects on Calcium- and Calmodulin-promoted Protein Phosphorylation

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