Identification of calmodulin in the green alga Mougeotia and its possible function in chloroplast reorientational movement

Abstract

A soluble protein was isolated from Mougeotia by chloropromazine-sepharose 4 B affinity chromatography. The protein matches the properties of calmodulin in terms of heat stability, Ca²⁺-dependent electrophoretic mobility in sodium-dodecyl-sulfate polyacrylamide gels, and its ability to activate cyclic nucleotide phosphodiesterase in a Ca²⁺-dependent manner. Phytochrome-mediated chloroplast reorientational movement in Mougeotia was inhibited by the calmodulin antagonist trifluoperazine, a hydrophobic compound, or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a hydrophilic compound; 50% inhibition (IC₅₀) of chloroplast movement is caused by 20–50 μmol l^-1 trifluoperazine or 100 μmol l^-1 W-7. The Ca²⁺-calmodulin may act as an intermediate in the chloroplast reorientational response in Mougeotia governed by phytochrome.