Identification of naturally occurring calmodulin inhibitors in plants and their effects on calcium- and calmodulin-promoted protein phosphorylation.
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 C18-microbondapak 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.
Paliyath
G
G
Department of Horticulture and Landscape Architecture, Washington State University, Pullman 99164-6414, USA.
Poovaiah
B W
BW
D000975:Antioxidants / Q000494:pharmacology; D002109:Caffeic Acids / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002147:Calmodulin / Q000037:antagonists & inhibitors* / Q000494:pharmacology / Q000502:physiology; D002392:Catechin / Q000494:pharmacology; D005419:Flavonoids / Q000032:analysis* / Q000494:pharmacology / Q000502:physiology; D010636:Phenols / Q000032:analysis*; D010726:Phosphodiesterase Inhibitors / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology; D010940:Plant Proteins / Q000032:analysis / Q000378:metabolism*; D019685:Rosales / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology
D000975:Antioxidants; D002109:Caffeic Acids; D002147:Calmodulin; D005419:Flavonoids; D010636:Phenols; D010726:Phosphodiesterase Inhibitors; D010936:Plant Extracts; D010940:Plant Proteins; D002392:Catechin; D002118:Calcium; C040048:caffeic acid